Are you positive it was a familiar Games Workshop produced? Their line of familiars was actually pretty small.
The thing about familiars is that any scale model could be used if it's small enough so it's hard to determine if what you saw was actually
GW. Their dragon here isn't a skeleton, and it doesn't have a leash, but I'm pretty sure it's the only baby drake they made specifically for pets/fams. It may have just been a model from a boxed game or separate kit altogether that was used as a familiar: