'73 A-Body caliper backing plates

I have a pair of 1973 Dodge Dart disc brake spindles and upper control arms. I want to put these in my 1967 Barracuda, all drum SL6.

I can get most of the brake parts from Kragen/O'Rilley's (loaded calipers from Cardone, rotor/hub assembly from Bendix, wheel bearings, etc). but I can't seem to be able to find backing plates for the calipers.

Where could I find some? Thanks for the help! :D