Another option, perhaps not good enough, but figured I'd throw it out there if you get desperate....

I have a RC-500 (same general layout -- it came with my HU) and it is a very light thing. If folks were into taking the risk, I could get some of the RC-600s from Crutchfield and repackage them (just with instructions, no box, no batteries) and send them on via non-trackable plain-old-mail in a bubble-pack envelope say with a cardboard stiffener.

If that would be an option I could check the postal rate tomorrow at my mail drop.