Well, I drug home another one

TT5.9mag said

Rock auto had cardone Kelsey Hayes calipers in stock. I ordered them today along with all of the hoses. Who has stainless pistons for them?

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Its been a while since I looked. If not listed under mopar, look under Mustang. Same piston. Also some Corvettes.
Quick look at some old links not finding them seperate but they may still be out there as this company is offering them installed.
http://calipersonline.com/compact1965-72.aspx
https://www.forabodiesonly.com/mopar/threads/removing-seized-kelsey-hayes-pistons.434769/
Might see your local parts store if you still have one.