I'm not clear on what you mean by a "parts manual" - it would have to be huge to include every single part used in a DP. But you can get wiring & plumbing schematics direct from American Coach Customer Service, and contact their parts dept on any given thing you need. They can often supply it, or tell you what the original part was and who supplied it.
REV Group had a parts look-up on their website for awhile, but not sure if it is up and available now. You can try to get access here: