You can buy surplus containers all day. Everything the military buys is contractual, they order X parts and get X parts and then put out a new bid contract 3 years later. The original manufacturer may not even make that part anymore, so there is no use in returning containers. They are just another part of the contract, built into the price, and they get sold off as surplus or scrap metal once the items inside are used up. It's wasteful but that's the way military contracting works. If you look closely at the container, it will have a contract number and a CAGE code. If it's new enough, the contract number should still be available and you can look it up online (usually just search the entire number) and it will tell you when it was ordered. The CAGE (Commercial and Governmental Entity) is the manufacturer, every business the government buys from has a unique 5-char ID.