Good point, I have, but forgot, that is an issue I had also. I went to the closest bigger PO and was able to cash it. I had her call to make sure they had the funds before driving there.
I would expect if you asked them to get the $, they would be obligated to cash the money order they, as a company made, if given time to get the cash needed. They get $ every day to cover the smaller daily stuff, She said they could increase it to cover the money order if I could wait a day.