A gun store? You could walk into Sears, K-mart, or Wards, or order from the JC Penny's catalog.
In my town, you could walk into one of the precursors of the modern "Convenience Store" (i.e. a gas station that sold other things, although these were more like a mini general store, than junk food heaven) and buy a rifle or a shotgun, or ammunition for them or for a handgun. (Holiday Stores, they even had a "house brand" of ammo)