the brake mountings on a disc axle are different to a drum axle.
I think rear discs were an optional extra just like ABS and only on certain models which may explain why they're rare?
if you have rear discs and no swaybar, think ur options are:
source a disc axle with swaybar mounts,
source a drum axle with swaybar mounts and convert the brake hose & handbrake cable to drums,
weld a simple custom swaybar mounting bracket to the current axle.