Little tiny 1 track (usually) demos that are mainly only sent to radio stations for airplay. Or... companies for some kind of promotional use. It's very VERY unlikely you'll find anyone selling these anywhere. And with only one track (that you could easily find on a single or album anyway) and little to no artwork, they're not even worth looking for. Unless you're one of those people who can't sleep knowing something in your collection is missing... You know who you are ;)