https://shop.usps.com/webapp/wcs/sto...WT.ac=10001641
The link above is the store section of the USPS website. I found this yesterday and I was shocked. I've been buying these small flat rate boxes for the last 6 months at the post office for about $5 each. I find this website and they deliver a pack of 10 or 25 boxes to you for free, no shipping cost either.
I still have a few days to see if they actually show up or not but I'm not happy that I've been buying these from the same "company" who gives them away. Why did no one there tell me?
If the link doesn't work for you, go to USPS.com, on one of the top bars click "buy stamps and shop" then click the box in the middle of the page that says "for mailing & shipping." From there you can pick from a number of different options, I chose "flat rate" to view the small flat rate box that many use for shipping razors.