Replacement leg motors for Roboquad?

Is there a source for secondhand parts for Roboquad, or motors that aren't factory-original but will work in the legs? My daughter dropped her Quad and one of the legs quit working. When my wife and I opened it up, and opened the case of the motor in that leg, a little cylindrical gear fell out in pieces. I'm guessing this is not something we can fix in place, but I don't want to buy a whole Quad just for one part if I don't have to...