Are you talking about real weapons? If so I don't think most suppliers will carry those now.
But, there are some heavy duty supply chains which sell the parts for guns what are called 'display model clearance sets'
Some of them probably don't even work, at least in any of their display tests. They are just there for possible Bee Bee gun sets, Paintball Guns, or just Guns without anything in them.
Finding actual firearms is a risky endeavor given governments don't ever want you getting a hold of such violent merchandise. But if on the other hand, you're needing an investor for regular or window-shopper type gun parts........There's lots of places that sell them. Hobbies stores sell tons of them. Online hobby stores carry overstocks especially places like Garts Brothers.