I have a bike that uses the old BMX/Cruiser standard 21.1 mm quill stem; it's a nice old Bianchi mountain bike that I'd rather like to keep going. Only problem is, I'm having a really hard time finding a stem that fits the bike, let alone one that fits me.

I know Wald makes those ugly steel things, and I've found a few old stems that work, but I haven't seen anything with enough reach for me.

I've found a quill extender that claims to be 21.1 mm; would I die if I tried to use that as a threadless adapter. Could I clamp a threadless stem (with a shim) onto it?

Does anyone actually make a threadless adapter for a 21.1 stem? Or any 21.1 stem aside from the Wald and the Sunlite?