If the original SSBC kit used stock Impala ss rear disc brakes to add to a fleetwood, then you can get loaded calipers, and rotors from Rock Auto. The loaded calipers I got from them not only had the pads, and guide pins, they also had the mounting bracket for the rear calipers. Took a couple days to get them, but I am sure they offer overnight delivery if you order them today.
2014 Chevrolet Silverado LTZ Z71 5.3 Aluminum V8 (My daily)
2007 Pontiac G6 VL 2.4 I4 (Wife's Daily)