PST still seems to carry them as part of their rebuild kit.
https://p-s-t.com/i-23162823-original-performance-super-front-end-kit.html#!year%3D1971%7C%7Cmake%3DPLYMOUTH%7C%7Cmodel%3DFURY%20III

at the time the whole kit from them was cheaper than 2 ball joints from rare parts. might still be.