You can trace a USPS money order for $5.20.
1. Must be 2 months or more since issue date.
2. You must present ID and money order stub.
If the money order has NOT been cashed they will refund by USPS check. If the money order has NOT been cashed, obviously, end of story.
If it has been cashed the USPS will send copies of the front and back of the money order. The copies will probably have the cashers bank information printed on it. This information could be helpful if you need to take further action. Hope this helps.