I cheated and did some hunting on United Connection 3.0 last night...

Found many more, and it was a hassle to get them...But I think some of them are only United Connection codes (not official city codes) used to distinguish the line of 'Any XXXX area airport', but do not work on at ual.com.

Here are a few:

QLA--All Los Angeles Area Airports (LAX, SNA, BUR, LBI, ONT)

QBA--All San Francisco Area Airports (SFO, OAK, SJC)

QMI--All Miami Area Airports (MIA, PBI, FLL)

Then a few oddball ones:

QNK--Any Kingston Jamaica Airport, KIN (Norman Manly Airport) and KTP (Tinson).

QKA--Any Maui Airport, OGG (Kahului) and JHM (Kapalua)

QBZ--Any Belize City Airport, TZA (Belize Municipal) and BZE (Belize Intl)

SDZ--Any Shetland Islands Airport, LSI (Sumburgh) and LWK (Tingwall)

And one legitimate one (I think):

GLA--Any Glasgow Airport, GLA (Glasgow Intl) and PIK (Preswick)

There were a few other even more remote ones (Sheltand Islands!?!?) that I didn't bother with.

Sorry, I couldn't sleep last night...A little too much free time on my hands.