[rvguy]

Adam

My comments are purely conjecture, perhaps they will spur fruitful sourcing for the rotors. 

One, I had great luck taking the actual part to a Prevost parts counter, and asking if they had ever used one on a Prevost. 

Two, that rotor and pads are unusual in that the rotor is asymmetric in thickness. Perhaps there is a symmetrical thickness rotor that could be substituted knowing the bolt pattern, diameter of rotor and thickness. Fleetpride has an online catalog with specific dimensions like that. 

Three, worst case is retrofit the tag disc brakes with the Bendix SB7 like are used on the fronts. Later year Newells used the SB7’s on both the drive and tag axles. Of course that would be calipers, mounts, and discs. 

Again, purely speculative on my part. Finding an exact replacement would be the best and easiest.

I am currently looking at the fleetpride catalog, hopefully I will run into something that will cross over or can be machined. I will try the prevost thing.  I will look into the sb7 change over ( sounds like a pain in the a--)