Do you mean solid metal? I'm not aware of anyone who makes them (with the exception of the front dogbone), but it wouldn't be too hard for an experienced fabricator to weld some up.
I've thought about it before, I think the best way to do it would be to weld circular pieces on the sides of the stock shells, then drill through the middle and weld in the sleeve for the bolt to pass through. If it was a serious car, I think it would be pretty bad ass.