Go underneath the coach and look at the casting number on the calipers. Then you can check at NAPA or rockauto.com. The front and rears MAY be the same or they may be different. You may even have drum brakes on the rear.
It is unfortunate but it seems any of the people that you talk to at an auto parts store won't have the slightest idea of how to help you when it comes to parts for an RV. Once you have the casting number, you can do a search online and find several sources.
For the rotors, be sure to count how many lugs you have, because they have several different types.