I came across this randomly while trying to find large hampers and apparently you can literally stock up on your own USPS supplies from Postal Products Unlimtied. You don’t even need to work at the United States Post Office. Buy uniforms, mail carts, mail bags, sorting supplies, and if you have enough money, even facility equipment for sorting mail too!

Definitely a peculiar find but some of their sorting gear is useful and not that expensive!