I haven't rebuilt these exact calipers before, but for my brakes, the rebuild kit came with piston seal, rubber piston boot and the wire ring to hold the boot on. I jsut ripped them apart, replaced the bits that cam e with the kit and reassembled. Be careful not to scratch the pistons as they come out though.
As for where to get them... not sure. I rang the usual suspects, Burson's, Repco and a bunch of Mazda dealers (they're Mazda brakes).