Dave,

There are (or at least were) replacement pistons available through Mopar. I think I have the part number somewhere, I'll try and find it.

But the easiest way to go is to purchase rebuilt calipers at Murrays, PepBoys or Autozone. As I recall Murrays had the best price - ~ $20 each with a core. I've been going this route for the last 2-3 years and have had great luck, the calipers work as well and last every bit as long as when I rebuilt them myself. Every store I've ever called has them in stock - including the one on Dixie when I blew out a caliper during a race weekend!