Sarracenia NW also sells live strands when they have it in stock. It's like $6 for a quart, I believe. You can grow plenty of live sphagnum on your own by placing a few live strands on a bunch of damp LFS, covering it with clear plastic, and putting the whole thing under light. It a month or two every segment of live sphagnum that went in should have grown into a large strand, and each strand can be divided. If you get any plants potted with live sphagnum, you can pinch the growing tips off it and have enough bits to start a stock of moss. Humid potted terrariums where the bottom of the tank is constantly wet also make great places to raise live sphagnum. Starting live strands from the dead stuff is an option, but a few bits of live stuff will really speed up the process if they're available.