Haha. This is a good one. They used to (maybe still) not allow 3rd party sellers like eBay, but Amazon has been used for a long time. I'm not sure why one was okay but not they other. Anyway, they would take a big operational hit, if they couldn't use Amazon.
Say a system goes down during a critical time, either training or a real mission. They need a part that they could order overnight and have it up by morning or maybe sooner if it's on that Amazon now thing. Or they could wait and try to source it out. Hope you can contact them, depending on the time. A lot of places that make equipment for the government have business hours. Depending on contracts and everything there would be a lot to get into, but the point is buying for Amazon is sometimes the best place to get the item from in a quick manner.