If you want ifo. on the availability and cost of replacement brake parts, visit the brakes/suspension forums.
The calipers are available, not too expensive, and the rotors are a bit more rare, but you can find these online, including e-bay.
Please keep in mind that when you search for rotors that you search for all A-body Mopars from 1965 - 72 if you do not find these for your specific year.
I posted summary info. on the prices and availability a while back, so visit that forum for info.