My husband has been going to send out Money orders to some 15 people once a month for me.
He first has to generate the envelopes, then go to the bank and spend some 1 1/2 hours getting checks of varying amounts printed, (which pisses the bank off but such is life), then match the checks to the envelopes and go to the post office.
This is a small volume mailing of money orders, and he hates it and the bank hates it. The people getting the checks love it though. 
I am not sure about finding a bank to process huge numbers of money orders.