Re: Difficult to find models
A lot of UAL aircraft are done by Gemini, and of those, a lot of those are done under contract for UAL (to be sold via their special airline shop.)
A lot of manufactures rarely ever re-release any Airline-Airframe combos they made before outside that condition. Most of them have this belief that if you didn't get it when they first did it, you should go suck on a lemon then, as they're museum pieces (to them). This also tends to create a artificial shortage of more desirable planes, which might also lead to not only making them hard to find, but also highly expensive compared to types like the UAL 777s and 747-400s, which Gemini gets contracts to make many times over, and has. I mean, imagine if Dragon did the American MD-80, or if Gemini Jets did the AA MD-80, you can see this model selling easily many times over, and each time when one shows up (like the JetX ones), they sold rather quickly. You have to remember, that these are also done once in a production run rather than continuoisly, like a Matchbox Skybuster has. So after 2000 examples (I think that's what GJ does), that's that for that release unless something prompts them to redo it.
I've looked at the database, and there are only 4 UAL 757s made in this hobby, 1 by herpa, and 3 by GJ, with only the last one in the CO/UAL hybrid, which was done last year. So pretty much all 1500 of those may have sold out quickly. Looked at some retailers I like to use, and no joy on the UAL 757-200. Seems like those sold out quickly, your best bet then will sadly be Ebay, or if you're lucky, a Trade Show (which California (mostly LA area)) tends to have a couple!
My Airport: Nowa Warszawa Int'l (NWL):
Attempt at first model airport (2005ish?)http://www.freewebs.com/nwlairport
Hey, model plane manufactures, how about some Braniff PZL 230Fs.