Must depend on where you are. We have a relatively new Gander Mountain here, and they have all kinds of pistols with shorter than 4" barrels--snubbies, Kahr's, xd subcompacts, etc. They also have a Beretta Storm at least and I'm not sure what else in "Assault Weapon" style, since they tend to be way overpriced and I figured there was no reason to even look.
Honestly, I don't see how they stay in business. My local one man one room shop almost always beats their price on firearms, often considerably. Their "sale" price on ammo tends to still be higher than the regular price at Walmart, and the local Dick's has wwb cheaper than Walmart. I pretty much go there so I can handle a specimen of a gun I'm considering, then order from my local guy.