How do people get military S&G padlocks?

[NNFAK]

I was just wondering how people get these from the military? Just to make it clear, I know you can buy them off eBay I just want to know how someone gets one in the first place and why do the military lay them off even though they still work?

[Riyame]

They get better versions such as the 951 replacing the 833 or when somebody looses a key for instance, they have to replace the lock and sometimes people walk off with them. Sometimes they "fall off" of the back of the truck or they are taken by somebody when a base is being decommissioned.