When it comes to postal service uniforms, the answer is a murky one at best. Officially, USPS does not sell uniforms to the public.
However, there are a few unofficial sources that sell them.
In theory, anyone could purchase a USPS uniform. However, in practice, it is more difficult than it sounds.
First of all, the price of a uniform is often prohibitively high, and even if someone could afford it, they would likely not be able to find a suitable one. Moreover, many people are uncomfortable wearing uniforms, no matter how official they may feel.
Ultimately, it is unlikely that anyone will be able to buy a USPS uniform. However, the idea remains a bit of a curiosity, and for some people it may provide a sense of solidarity with the postal service.