Yes definitely FREE from PO. If you print your own International Labels using Mypost account with AP those plastic envelopes are designed to fit the labels. If your local PO doesn't have them maybe they will get them in for you? Just picked up bundle of 50 from my local.

Unfortunately you just have to be really determined to get some of the items or functions that AP constantly advertise, we have found that many times the person behind the counter has no idea what is available or what they have in stock.

Very poor training on AP's or the Managers part.  Be persistent.