72 Demon Power Steering Gearbox/Coupler Help...?

I know everybody uses the u joints and says they have no problem, but since they don't accommodate body flex, I won't touch em. A failure there is guaranteeing an accident.

Contact Rick Ehrenberg at mopar action (formerly the magazine). He has a stash of parts and also knows a ton of people.
If it was me, I'd pm Tony Defeo, and get one there, and get a rebuild kit if necessary.