71 Dart Camber Issues

Most likely is probably a worn out lower control arm bushing, or even a cracked/broken LCA pivot pin mount in the K frame.

Of course its also possibly that the shop that did the alignment didn't torque the camber bolts properly and one or both of them backed off, but that's a lot less likely than just worn out bushings etc.

Sounds like its time to rebuild the front end. I'd take apart that side first, and inspect everything as you go. Pay special attention to the upper and lower control arms. Most likely its just worn out bushings and mounts, but there's always the possibility that something is cracked/broken.