There were a number of them,Ye Old Western Hunter, Numrich Arms, Potomac Arms, and more. When you ordered from them, they sent your the products by U.S. Mail. In Old America, people were called citizens and they could purchase firearms without governmental oversight.
The picture is from Klein's. Before you start drooling over the prices, remember that $100.00 in 1963 is comparable to $815.00 today. Add to that the availability of mil-surp guns in the decades after WWII and the prices are not that remarkable. It's the freedom you should be remembering.
They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
-- Benjamin Franklin, Historical Review of Pennsylvania, 1759