The suggestions you've probably already read are the best ones
miracool / ironall paper are both the same thing. newmilfordphoto sells it as well as a few other sources.
Here's a couple of past threads with wholesale sources listed:
http://www.t-shirtforums.com/showthread.php?t=5670
http://www.t-shirtforums.com/showthread.php?t=3459