Rick
We have 3 Skymasters with the 18X5.5 tires and large brake calipers. You can order all the parts from any Clevland dealer. You can bet it won't be cheap, We just replaced one of our calipers, our cost was @$850.00 But it even included the attachment forging that goes on the axle stub. The caliper itself does not have return spings inside, but with metallic pads the rolling friction is almost nothing. Email me if you want part numbers.
kimgeyer@carolinastainedglass.com
Kim