If you crush these and mix them with cooked rice, you get rice wine.
I'm not sure what's actually in these. They certainly contain yeast, but I think also some kind of kōji (I don't think yeast alone could do much with rice).The rice is, I think, allowed to naturally develop mold before it's ground and pressed into balls.
I've been able to find these at one of the grocery stores near Main and Hastings, but had to root around quite a bit. Best to bring the bag in and show the shopkeeper.