ABE ATL AUS BDL BNA BOI BOS BTV BUR BWI CLD CLE CLT DAL DCA DEN DFW DSM DTW ELP EWR FAT GNV HOU IAD IAH ITH JAX JFK LAS LAX MCO MDT MDW MEM MHT MKE MSN MSP OAK ORD PDX PHL PHX PIT PNS SAN SAT SBA SEA SFO SJC SLC TPA TUS
AMM ARN ATH BCN BGA BGO BHX BMA BOG BRU BSL BUD CDG CHQ CPH DUS FCO FRA GIG GVA HER IST LCA LHR LIN LJU MAD MJT MUC MXP NCE OSL PTY SKG SKP TLV YYZ ZRH
Just added the ones in bold after our last family vacation. Up to 55 domestic and 38 international. Love that I'm starting to get more and more anagram / single-letter-swap code chains going, but I think connecting YYZ to the rest is gonna be a bit tricky.