The GC rear discs have a caliper bracket that bolts to the rear end housing. Those, the dust shields, and most of the parking brake hardware are going to be salvage yard items. You can also use Jeep Liberty rear discs, they have a little beefier rotor and pad (the early ones are still 5x4.5- what year the cutoff is I don't recall offhand). You will need to fab up some cable adaptors for the parking brake linkage with whichever ones you use.
Since they are floating calipers, you will need consider how you will anchor the rubber brake hoses to the rear end housing, maybe cut those brackets off the Jeep while you're at the boneyard getting the caliper brackets and other stuff.