погулять здесь, может перекрёстные ссылки куда-нибудь и приведут
http://www.flightstats.com/go/ ...

NYC - New York
CHI - Chicago
SEL - Seoul
TYO - Tokyo
BER - Berlin
ROM - Rome
MIL - Milan
LON - London
PAR - Paris

и т.д. Как видим, часто это первые три буквы в названии города. Вообще, не так уж много городов с несколькими аэропортами, европейские я по-моему вообще все перечислил.
Смотрел на сайте opodo.de хитрым способом - вводится в графе "из" целиком название города с несколькими аэропортами, код которого хотим узнать, а в графе "в" название несуществующего пункта. Тогда в след. окне появляется вот этот самый мультикод. А где список найти, я не знаю.

AG Solomon Islands AGGA * AUKI AGSolom
AG Solomon Islands AGBT * BATUNA AGSolom
AG Solomon Islands AGBA * BARAKOMA AGSolom
AG Solomon Islands AGGB * BELLONA AGSolom
AG Solomon Islands AGGQ * ONTONG JAVA AGSolom
AG Solomon Islands AGAR * ARONA AGSolom
AG Solomon Islands AGGM * MUNDA AGSolom
AG Solomon Islands AGGI * BABANAKIRA AGSolom
AG Solomon Islands AGOK * GATOKAE AGSolom
AG Solomon Islands AGGV * SUAVANAO AGSolom
AG Solomon Islands AGAT ATOIFI AGSolom
AG Solomon Islands AGGK * KIRAKIRA AGSolom
AG Solomon Islands AGGU * MARAU AGSolom
AG Solomon Islands AGTI * TULAGHI HELIPORT AGSolom
AG Solomon Islands AGGC * CHOISEUL BAY AGSolom
AG Solomon Islands AGGH HONIARA (HENDERSON) AGSolom
AG Solomon Islands AGGO * MONO AGSolom
AG Solomon Islands AGGN * GIZO AGSolom
AG Solomon Islands AGGF * FERA AGSolom
AG Solomon Islands AGGJ * AVUAVU AGSolom
AG Solomon Islands AGGY * YANDINA AGSolom
AG Solomon Islands AGNA * NANA AGSolom
AG Solomon Islands AGVH * VIRU HARBOUR AGSolom
AG Solomon Islands AGRC * RINGI COVE AGSolom
AG Solomon Islands AGGE * BALLALAE AGSolom
AG Solomon Islands AGAF * AFUTARA AGSolom
AG Solomon Islands AGEV * GEVA AGSolom
AG Solomon Islands AGGR * RENNELL AGSolom
AG Solomon Islands AGGL * SANTA CRUZ AGSolom
AG Solomon Islands AGGP * PARASI AGSolom
AG Solomon Islands AGIN * ISUNA HELIPORT AGSolom
AG Solomon Islands AGGT * SANTA ANNA AGSolom
AG Solomon Islands AGMU * MALU'U HELIPORT AGSolom
AG Solomon Islands AGGS * SEGHE AGSolom
AG Solomon Islands AGRM * RAMATA AGSolom
AG Solomon Islands AGKW * KWAILABESI AGSolom
AG Solomon Islands AGKU * KUKUDU AGSolom
AG Solomon Islands AGKG * KAGHAU AGSolom
AU Nauru AUUU NAURU I. AUNauru
AY Papua New Guinea AYVN * VANIMO AYPapua
AY Papua New Guinea AYKM * KEREMA AYPapua
AY Papua New Guinea AYKI * KIUNGA AYPapua
AY Papua New Guinea AYKY * KUNAYE AYPapua
AY Papua New Guinea AYMO * MOMOTE AYPapua
AY Papua New Guinea AYWD * WAPENAMANDA AYPapua
AY Papua New Guinea AYMS * MISIMA AYPapua
AY Papua New Guinea AYHK * HOSKINS AYPapua
AY Papua New Guinea AYMD MADANG AYPapua
AY Papua New Guinea AYMH MOUNT HAGEN AYPapua
AY Papua New Guinea AYKK * KIKORI AYPapua
AY Papua New Guinea AYWK WEWAK AYPapua
AY Papua New Guinea AYTK TOKUA AYPapua
AY Papua New Guinea AYNZ NADZAB AYPapua
AY Papua New Guinea AYCH * CHIMBU AYPapua
AY Papua New Guinea AYTA * TARI AYPapua
AY Papua New Guinea AYTB * TABUBIL AYPapua
AY Papua New Guinea AYGN * GURNEY AYPapua
AY Papua New Guinea AYDU * DARU AYPapua
AY Papua New Guinea AYBK * BUKA AYPapua
AY Papua New Guinea AYGA GOROKA AYPapua
AY Papua New Guinea AYKA * KIRIWINA AYPapua
AY Papua New Guinea AYGR * GIRUA AYPapua
AY Papua New Guinea AYMN * MENDI AYPapua
AY Papua New Guinea AYMR * MORO AYPapua
AY Papua New Guinea AYPM PORT MORESBY ACC/FIC/COM AYPapua
AY Papua New Guinea AYPY PORT MORESBY AYPapua
AY Papua New Guinea AYKV * KAVIENG AYPapua
BG Greenland BGGL SONDRESTROM FIR BGGreen
BG Greenland BGTQ * TASIUSAQ (NANORTALIK) BGGreen
BG Greenland BGQK * QASSIARSUK BGGreen
BG Greenland BGIO * IGALIKO BGGreen
BG Greenland BGIL * ILIMANAQ BGGreen
BG Greenland BGET * EQALUGAARSUIT BGGreen
BG Greenland BGTA * TASIUSAQ (UPERNAVIK) BGGreen
BG Greenland BGUQ UUMMANNAQ/QAARSUT BGGreen
BG Greenland BGLL * ILLORSUIT BGGreen
BG Greenland BGAQ * AAPPILATTOQ/NANORTALIK BGGreen
BG Greenland BGJN ILULISSAT BGGreen
BG Greenland BGMO * MORIUSSAQ BGGreen
BG Greenland BGFH PAAMIUT (HEL) BGGreen
BG Greenland BGNO * STATION NORD (MIL) BGGreen
BG Greenland BGBW NARSARSUAQ BGGreen
BG Greenland BGAM * AMMASSALIK BGGreen
BG Greenland BGAP ALLUITSUP PAA BGGreen
BG Greenland BGSO * SAARLOQ BGGreen
BG Greenland BGST * SAATTUT BGGreen
BG Greenland BGAA AASIAAT BGGreen
BG Greenland BGKQ * KULLORSUAQ BGGreen
BG Greenland BGAT * ATTU BGGreen
BG Greenland BGTN * TINITEQILAAQ BGGreen
BG Greenland BGSG * SERMILIGAAQ BGGreen
BG Greenland BGGH NUUK BGGreen
BG Greenland BGNU * NUUSSUAQ BGGreen
BG Greenland BGKM * KUUMMIUT BGGreen
BG Greenland BGKA * KANGAATSIAQ BGGreen
BG Greenland BGSV * SAVISSIVIK BGGreen
BG Greenland BGSF KANGERLUSSUAQ BGGreen
BG Greenland BGKS * KANGERSUATSIAQ BGGreen
BG Greenland BGGD KANGILINNGUIT BGGreen
BG Greenland BGAG * AAPPILATTOQ/UPERNAVIK BGGreen
BG Greenland BGNN NANORTALIK BGGreen
BG Greenland BGUM * UUMMANNAQ BGGreen
BG Greenland BGIS * ISORTOQ BGGreen
BG Greenland BGNQ * NUUGAATSIAQ BGGreen
BG Greenland BGSC * ITTOQORTOORMIIT BGGreen
BG Greenland BGAK * AKUNAQ BGGreen
BG Greenland BGIT * IKAMIUT BGGreen
BG Greenland BGKL * UPERNAVIK KUJALLEQ BGGreen
BG Greenland BGCO NERLERIT INAAT BGGreen
BG Greenland BGPT PAAMIUT (AD UNDER CONSTRUCTION) BGGreen
BG Greenland BGQQ QAANAAQ BGGreen
BG Greenland BGIG * IGINNIARFIK BGGreen
BG Greenland BGFD * NARSAQ KUJALLEQ BGGreen
BG Greenland BGIN * INNARSIUT BGGreen
BG Greenland BGAS * AMMASSIVIK BGGreen
BG Greenland BGMV * MESTERVIG (MIL) BGGreen
BG Greenland BGUK UPERNAVIK BGGreen
BG Greenland BGUT * UKKUSISSAT BGGreen
BG Greenland BGSQ * SAQQAQ BGGreen
BG Greenland BGDH * DANMARKSHAVN (Private AD) BGGreen
BG Greenland BGDB * DANEBORG (MIL) BGGreen
BG Greenland BGMQ MANIITSOQ BGGreen
BG Greenland BGNS NARSAQ BGGreen
BG Greenland BGAR * ARSUK BGGreen
BG Greenland BGIA * IKERASAK BGGreen
BG Greenland BGSS SISIMIUT BGGreen
BG Greenland BGNL * NALUNAQ BGGreen
BG Greenland BGQE * QEQERTAQ BGGreen
BG Greenland BGNT * NIAQORNAT BGGreen
BG Greenland BGNK * NIAQORNAARSUK BGGreen
BG Greenland BGGN * QEQERTARSUAQ BGGreen
BG Greenland BGKK KULUSUK BGGreen
BG Greenland BGIK * IKERASSAARSUK BGGreen
BG Greenland BGTL THULE AIR BASE (MIL) BGGreen
BG Greenland BGSI * SIORAPALUK BGGreen
BG Greenland BGQT * QASSIMIUT BGGreen
BG Greenland BGJH QAQORTOQ BGGreen
BG Greenland BGKT * KITSISSUARSUIT BGGreen
BG Greenland BGCH * QASIGIANNGUT BGGreen
BG Greenland BGPC * IKERASASSUAQ BGGreen
BI Iceland BISR * STORIKROPPUR BIIcela
BI Iceland BIBR * BUDARDALUR BIIcela
BI Iceland BIBF * BORGARFJORDOUR EYSTRI BIIcela
BI Iceland BIIS * ISAFJORDUR BIIcela
BI Iceland BIEG * EGILSSTADIR BIIcela
BI Iceland BIHK * HOLMAVIK BIIcela
BI Iceland BIVH * VARMAHLID BIIcela
BI Iceland BIST * STYKKISHOLMUR BIIcela
BI Iceland BISK * SKOGASANDUR BIIcela

BI Iceland BISV * SKALAVATN BIIcela
BI Iceland BIBK * BAKKAFJORDUR BIIcela
BI Iceland BIPA * PATREKSFJORDUR BIIcela
BI Iceland BIAR * AKUREYRI BIIcela
BI Iceland BIVI * VIK BIIcela
BI Iceland BISI * SIGLUFJORDUR BIIcela
BI Iceland BITM * THORSMORK BIIcela
BI Iceland BIVA * VATNSNES BIIcela
BI Iceland BISS * SANDSKEID BIIcela
BI Iceland BISP * SPRENGISANDUR BIIcela
BI Iceland BISN * SVINAFELL BIIcela
BI Iceland BIBV * BREIDDALSVIK BIIcela
BI Iceland BIHU * HUSAVIK BIIcela
BI Iceland BISF * SELFOSS BIIcela
BI Iceland BIGJ * GJOGUR BIIcela
BI Iceland BIGE * GEYSIR BIIcela
BI Iceland BIFL * FLUDIR BIIcela
BI Iceland BIDA * DAGVERDARA BIIcela
BI Iceland BIDV * DJUPIVOGUR BIIcela
BI Iceland BIKP * KOPASKER BIIcela
BI Iceland BIVO * VOPNAFJORDUR BIIcela
BI Iceland BITN * THORSHOFN BIIcela
BI Iceland BISA * SANDA BIIcela
BI Iceland BITE * THINGEYRI BIIcela
BI Iceland BIBL * BLONDUOS BIIcela
BI Iceland BIHN * HOFN/HORNAFJORDUR BIIcela
BI Iceland BIGH * GUNNARSHOLT BIIcela
BI Iceland BIMM * MELGERDISMELAR BIIcela
BI Iceland BINF * NORDFJORDUR BIIcela
BI Iceland BIRG * RAUFARHOFN BIIcela
BI Iceland BIRF * RIF BIIcela
BI Iceland BIAE * ARNGERDAREYRI BIIcela
BI Iceland BIKF KEFLAVIK AIRPORT, APP/TWR, OPS, MET BIIcela
BI Iceland BIBA * BAKKI BIIcela
BI Iceland BIGR * GRIMSEY BIIcela
BI Iceland BITA * REYKJAVIK POST AND TELEGRAPH ADMINISTRATION BIIcela
BI Iceland BICC REYKJAVIK GUFUNES COM CENTRE BIIcela
BI Iceland BIRD REYKJAVIK FIR, OAC, ACC, FIC BIIcela
BI Iceland BICA REYKJAVIK CIVIL AVIATION ADMINISTRATION BIIcela
BI Iceland BIRK REYKJAVIK AIRPORT, NOF, MET BIIcela
BI Iceland BIKR * SAUDARKROKUR BIIcela
BI Iceland BIFM * FAGURHOLSMYRI BIIcela
BI Iceland BIMS * TUNGUBAKKAR BIIcela
BI Iceland BIKE * KERLINGARFJOLL BIIcela
BI Iceland BIKA * KALDARMELAR BIIcela
BI Iceland BIND * NYIDALUR BIIcela
BI Iceland BIMK MULAKOT BIIcela
BI Iceland BIHZ * HUSAFELL BIIcela
BI Iceland BIRE * REYKHOLAR BIIcela
BI Iceland BIGS * GRIMSSTADIR BIIcela
BI Iceland BIHX * HRAUNEYJARFOSS BIIcela
BI Iceland BIRL * REYKJAHLID BIIcela
BI Iceland BIHR * HVOLVOLLUR BIIcela
BI Iceland BIHV * KROKSSTADARMELAR BIIcela
BI Iceland BIHI * HVERAVELLIR BIIcela
BI Iceland BIRS * REYKJANES BIIcela
BI Iceland BIHL * HELLA BIIcela
BI Iceland BIVM * VESTMANNAEYJAR BIIcela
BI Iceland BIKL KIRKJUBAJARKLAUSTUR BIIcela
BI Iceland BIHE * HERDUBREIDARLINDIR BIIcela
BK United Nations Interim Administration Mission in Kosovo (UNMIK) BKPR PRISTINA AIRPORT, UNMIK (ON A TEMPORARY BASIS) BKUnite
CU Canada CUUP OTTAWA/UPLANDS CFB, ONT CUCanad
CW Canada CWVR VANCOUVER (PACIFIC WEATHER CENTRE), B.C. CWCanad
CW Canada CWEG EDMONTON (ALBERTA/ARCTIC WEATHER CENTRES), ALTA CWCanad
CW Canada CWIS OTTAWA (AES ICE FORECASTING CENTRE), ONT. CWCanad
CW Canada CWHX BEDFORD (ATLANTIC WEATHER CENTRE), N.S. CWCanad
CW Canada CWWG WINNIPEG (PRAIRIE WEATHER CENTRE), MAN. CWCanad
CW Canada CWTO TORONTO (ATMOSPHERIC ENVIRONMENT SERVICE HQ), ONT. CWCanad
CW Canada CWAO MONTREAL (CANADIAN MET CENTRE), QUE. CWCanad
CW Canada CWUL MONTREAL (QUEBEC FORECAST OFFICE), QUE. CWCanad
CY Canada CYPR PRINCE RUPERT, B.C. CYCanad
CY Canada CYFJ * LA MACAZA, QUE. CYCanad
CY Canada CYAC * CAT LAKE, ONT. CYCanad
CY Canada CYCG CASTLEGAR, B.C. CYCanad
CY Canada CYCA * CARTWRIGHT, NFLD. CYCanad
CY Canada CYDB * BURWASH, Y.T. CYCanad
CY Canada CYYL LYNN LAKE, MAN. CYCanad
CY Canada CYXS PRINCE GEORGE, B.C. CYCanad
CY Canada CYMA MAYO, Y.T. CYCanad
CY Canada CYXT TERRACE, B.C. CYCanad
CY Canada CYXR EARLTON(TIMISKAMING REGIONAL), ONT. CYCanad
CY Canada CYTJ * TERRACE BAY, ONT. CYCanad
CY Canada CYTS TIMMINS, ONT. CYCanad
CY Canada CYTR TRENTON, ONT. CYCanad
CY Canada CYWJ * DELINE, N.W.T. CYCanad
CY Canada CYAM SAULT STE. MARIE, ONT. CYCanad
CY Canada CYHU MONTREAL/ST-HUBERT, QUE CYCanad
CY Canada CYXE SASKATOON/JOHN G. DIEFENBAKER, SASK. CYCanad
CY Canada CYMX MONTREAL INTL (MIRABEL), QUE. CYCanad
CY Canada CYXD EDMONTON MUNI, ALTA. CYCanad
CY Canada CYYU KAPUSKASING, ONT. CYCanad
CY Canada CYUL MONTREAL/PIERRE ELLIOT TRUDEAU INTERNATIONAL AIRPORT CYCanad
CY Canada CYPA PRINCE ALBERT, SASK. CYCanad