I was thinking about it and I don't know...it seems that it would be cheaper for the orgs to cut out the middle-man (or woman) and just purchase them for themselves. Even if they didn't have a "store" per se, they could hold onto them and sell them as needed.
There are a number of places that do them but few have Greek letters. Usually, you'd have to get the words printed out. Example:
http://www.pinsource.com/home/en/new..._your_own.html