When it became legal to sell guns in that particular country.
Almost as soon as they were invented. Cost and/or laws kept many from acquiring one, but, they were popular.
In 1938 this submachine gun became popular with the U.S. Military, which they utilized during World War II. Today these guns are collected by many gun enthusiasts, and are worth between $25,000 and $40,400.
You can buy used gun safes in the US in many different places. Amazon and eBay are popular places that people often buy these type of cases at. Gun stores also sell used gun safes.
The hidden gun is most likely made up. People have made deadly hidden guns though, so it is a real weapon, just not popular or avalible in stores.
Gun stores, pawn shops.
Try the yellow pages and look for auction houses, antique stores, gun stores.
Gun stores, gun shows, pawn shops, sporting goods stores, want ads, garage sales.
Toysrus
Gun shops, gun stores, sporting goods stores, ammunition retailers, internet
gun stores, auctions..... many more Gun shows
sometimes gun stores will buy them of you
Vet supply stores or rancher supply stores.