I'd second Binko's statement, look seriously at a Birmingham boxlock. I "went down the same road" a couple years ago, ended up with a Webley and Scott 2 1/2" 12 ga. built in 1909-10. Shooting 7/8 and 1 oz. loads the grouse don't know the difference and I got a nifty little gun, 6#, 3 oz. for a little over a grand. I handload, mostly for the love of it, but even in Colorado one can find 2 1/2" on the shelves of a couple stores in Denver--Reynolds and BassPro. If you have a Cabela's within driving distance, the ones I've been in carry 2 1/2" as well. Good luck!
Steve