It depends mostly upon the feed mechanism. Some guns, such as the venerable Marlin 39A, will feed Short/Long/Long Rifle. A standard 10/22 will not. I think Marlin 60's are strictly Long Riflel, as well. But there are other guns which can handle the Short, although they are going to be used. These would be many of the pump action guns, some Mossberg bolt actions, maybe the Winchester 9422. Oh, yeah, can't forget the Remington 550 semi-auto, precursor to the Remington 552 Speedmaster, a current gun which will handle all three loadings. 10/22 Short conversion kits such as the VQ Firefly can also be purchased. And any single shot chambered for Long Rifle will shoot Shorts and Longs, plus you can single-load any Long Rifle gun by hand.
The only caveat with Shorts in a gun chambered for Short/Long/Long Rifle is that they may not be as accurate, since these usually have a twist designed for a 40 grain bullet VS the Short's 29 grainer, and a steady diet of Shorts in the slightly longer chamber can foul it up badly or sometimes erode it, making Long Rifle rounds hard to load/extract.
A super gun fun would be a Browning take down in Short, although it will be pricey.
Upon re-reading your post, the three stores you went to weren't necessarily the most likely to be familiar with guns. Gone are the days of the local hardware store which sold traps, rifles, fishing gear, etc. My local Dick's gun department is ignorant in many areas. Pawn shops are only as good as the guy behind the counter who may have been painting houses last week. Heck, even some gun shops are weak when it comes to rimfires. Best to do some reading and check out
http://www.RimFireCentral.com.