Rebuild?
Hey Pete,
Just an FYI-- If you still have the caliper, it can most likely be rebuilt. Rebuild kits are fairly cheap and the job is fairly easy, and unless your piston bores are very damaged, it's the way to go.
If you're not into doing it yourself, any shop should be able to handle rebuilding a caliper with little issue.
Unfortunately, a used caliper may have the same problems that you currently have...
Either way, good luck!