They come in a bag, individually wrapped, you can find the Japanese mochi in most Asian markets (isle perhaps). (Kakumochi) http://en.wikipedia.org/wiki/Zōni Zoni Mochi.

The way we prepare it in Japan is we place the mochi in the toaster oven, it’s gets crunchy on the outside warm and soft on the inside, and put a dabble of soy sauce/butter when finished, some use cheese, some deep fry it, some just bake it and add it to soups, etc. If you can’t find the package in your local grocer, they will most likely have it at the Japanese supermarket.