Buy Postal Money Order Online Official

: This is your only proof of purchase and is required to track or replace a lost order. Online Alternatives

: Bring cash or a debit card; credit cards and personal checks are not accepted.

Since you can't buy them online, here is the standard process for getting one at the Post Office:

If you need to send money digitally without visiting a physical location, consider these online-only services: Sending Money Orders - USPS