Going back a bit further:Print catalogs for companies like Brigade Quartermaster, the OLD Sportmans's Guide, Cheaper Than Dirt, US Cavalry.... Shotgun News..
The Martin B. Retting catalog shown above was dated 1953. But when I was going into their store in Culver City, Calif. in the 1960's, their prices weren't much higher. For example:
Note the first item on this page, the German T-Gewehr for $125.
Many of these firms selling war relics were located in the north east. Retting moved from NY to CA in 1953 so at least I could go to that one in person.
Another catalog I used to get was this one:
I'd send away for these based on advertisements I saw in Shotgun News, mostly. Another one I got was Der Alte Oberst, I think he was in La Jolla, Calif.