You are correct, 71-73 suspension and front brake parts are not that easy to come by.  I am in process of rebuilding the brakes and front end in my 73.  I have found all but the rotors.  The front calipers took 3 weeks to get.  The lower control arm bushings were second hardest to find.   

The 74 and up lower and upper control arms will not bolt onto your car without some modifications to the cross member.  The upper control arm bolts are spaced differently and the lower control arm bushing is longer.  I am not sure about the spindles but the ball joints look like they can be swapped from early to later.