: You can also order these supplies by calling the USPS Package Supply Center at 1-800-610-8734 . 2. FedEx and UPS

: You can find boxes for UPS Simple Rate at The UPS Store . Unlike USPS, UPS often allows you to use your own packaging for their flat-rate service as long as it meets their size requirements. 3. Third-Party Retailers where can i buy flat rate shipping boxes

: You can pick up a limited selection of Priority Mail Flat Rate Boxes at any local Post Office lobby. : You can also order these supplies by

: Retailers like Staples and Office Depot often carry flat rate boxes. They may provide them for free if you purchase shipping services through them, or they may sell them as part of their standard inventory. Unlike USPS, UPS often allows you to use

: Independent stores like PostNet or Mail Boxes Etc. typically stock various flat rate options and can help with packing.

If you need specific types of boxes or want to buy in bulk from other sources: