I lucked into it one time. I had asked if the LPS had any plants other than what they had in the tanks, and back in the back they had a breeder tank of guppies that had this moss in it.
They ended up selling me a wad of it for about $3.00. It grows great, but I've only kept it in tropical tanks. They said, though, that as long as it has light it'll do well.
If I were you I'd ask around for some. I know Betta breeders use it for their fry tanks. You may want to ask Sherri from http/www.bettadreams.com if she has any she'd send you.
If you havent found any in a while and would be interested let me know and I'll send you some if you want.