One of my rear calipers has locked up and is not working. I took it to the shop where they told me that I need to replace the rear calipers and I was just going to shop around for prices before before I bring it back but if anyone has theirs siting around after installing an AM brake kit then let me know and I may buy them off of you. I have an 06 and I'm looking for a set in good shape...

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There were a couple rear sets on ebay last time I looked, if you haven't checked there already.
Do you know exactly what locked up? The piston? More commonly, the upper slider tends to get stuck. Diagram below shows them as upper and lower cylinder slide pins, and the caliper slides in and out on these when the brakes are applied and released. If one or both are frozen, and not the piston, you may not need to replace the caliper.
Easy to check - remove the lower bolt (make sure that's not stuck in the rubber boot/slide bushing), and pivot the caliper upwards so it clears the rotor. It should pivot easily on the upper slider bolt, and should move in and out easily on the slider too. If the rubber boot is not locked onto the lip of the caliper, water gets into the slider pocket in the caliper and can cause it to seize on the slider bolt.
This happened to mine - had to replace the upper slider bolt only, was able to salvage the caliper. Cleaned it out, new bolt and correct type of grease, made sure the boot was on all the way - good to go.