Bachmanns garden centers sell small medium and large bales from $8 to $15 very good stuff way better than Mosser lee which often grows into other less desireable species of mosses... and ferns, liverworts, mushrooms and clovers... it's a neat way to get some interesting temperate northern bog plants by merely keeping it wet but not when all you want is pure spahgnum!
Here's my method for farming my own spahgnum moss:
Using a jiffy seedling tray punch holes in the bottom with a wide nail to allow air circulation and good drainage.
shred a few handfuls of the nice blonde colored LFSinto a bucket of water (Mosser Lee is dark brown and as stated full of twigs and even stones!). Sumbmerge it and squeeze it to absorb as much water as it can then squeeze out as much as you can so it's moist but fluffy and airy.
Drop it loosely into the seedling tray making and even layer only 1/2 -1" or so as you are only "seeding" the tray and giving the spores in the dried heads a substrate to germinate upon.
Put in a bright environment. My highland chamber grows sphagnum moss faster than anything! It seems to grow slower in the lowland tanks.
Mist the surface every couple days, don't dump water on it to keep it saturated just spray to keep it evenly moist. After about a month it should begin to raplidy change to green and within another month or two you'll have visible spahgnum headsover the surface. Just keep the routine and replace anything you take with new shreds of dried stuff and you'll have a continuously regenerating supply.
I remember one guy took this to the xtreme and filled a plastic little mermaid kiddie pool with it and made a huge batch in his back yard! I wish I had a yard...