Turner's has a few and other stores will occasionally have some on the shelf. But I can't think of anywhere in our area that has a *good* selection. I'd have to say mail order would be your best bet for access to a lot of good calls. If you can find Varmint Hunter magazine, Trapper and Predator Caller, Varmint Master, etc. you'll see lots of ads.
As far as what's best... good question. I'm of the opinion that any call will work at some time but none of them will work all the time. That's why most callers end up with a pretty good sized selection of different calls... just like bass fisherman and lures.
I'd agree. I end up picking one up every now and then and I've got a good 15-20 scattered between various hunting bags, coat pockets, glove boxes, etc. There are a couple that I go back to more often than others but that's largely arbitrary. Just about any call will make the noise that you need... or close enough to it. I called a coyote in once with a duck call blown really hard. We forgot the predator calls and only had that duck call. Had to blow hard to get it high enough but it worked.
Another time I forgot the calls (this isn't a habbit, really) and had to use a turkey diaphragm call. That was actually a good move. I prefer them now for bobcats. Not because of the sound but because it leaves you hands free and you need zero movement to make the noise. It works really well while bowhunting too.