I bought a new one for my wood lathe but it does more of a length wise round copy of objects and I was originally trying to find one more like a old key copier machine a friend of mines dad had for coping decoys witch where more of a out of round 3D shape, you could probably do a search for lathe copiers and find a store bought one for a metal lathe if its in the budget or look at the pictures and specs on some of the copiers and build one for your self
good luck
Robert