I'll be watching the response to this, as I was thinking about doing the same thing. Someone (from here?) had an article out there on the web that mentioned it, but with no details on growing it, from what I can remember.
Frog moss is great and I use it in the Winter all the time. In the Summer I go hiking in the woods, and gather some moss that are on the base of the trees. It's thick and beautiful, and use it in my outdoor enclosures. Lasts forever as long as you have plenty of humidity and mist often.