Like Angel Rice Leaven, I'm not sure what this stuff is. It certainly contains yeast, but may also contain mold (the rice is, I think, allowed to naturally develop mold before it's turned into flour). It would make sense for it to contain mold, because I don't see how yeast alone could do much with rice.
I found some of these at one of the Chinese grocery stores at Main and Hastings, in a box shoved deep into a shelf at the back of the store.