Right/Left hand replacement studs?

They are available. There aren't that many combinations of wheel studs. Many auto parts have trays of wheel studs in the back, especially an older family shop. It wasn't just Mopar that used LH threads on the driver's side. Some sites like Tire Rack list all the wheel bolt patterns and threads. I recall several 60's Japanese cars had LH threads. The kink is if he has the factory K-H disk brakes since those studs were special. There is a post in the last few months on those and where to buy.

Make the paint shop get them. No excuse for snapping studs. It takes an extreme torque to snap them, like jumping on a lug wrench. At least they didn't spin the studs, which would have messed up the hub or axle.