Paul,
You have two options. One of which is to buy hard copies of the books you need. Prevost will sell them, and you may come upon someone on this site or on ebay that will offer them for sale.
But the second option is free. If you found the service manual on line, you probably came through this page with is the gateway to a closet full of books, diagrams, recall notices, service bulletins, and even documentation on all the purchased components Prevost uses on your coach.
https://secureus5.volvo.com/technicalpublications/en/manuel.asp
The site is a little tricky to use and generally speaking the best way to start is to do a search for your needs by providing the minimum of information and then search. For your coach the service manual is accessed by selecting “XL MTH”, and “Service Manual”. If you want you can opt for a section to narrow your search, but when you select “search” you will also have the ability to focus on a specific topic or section.
Similarly you can search for and get pneumatic and electrical diagrams. For purchased components near the bottom left you can scroll through the choices and find information on just about all purchased parts.
I have used both hard copy and internet access and find I have created hard copy of items I may want for frequent reference, or reference when working on the bus such as the pneumatic diagram. But for other purposes I just use the access to the publications via my computer and will print out a copy if needed of a page or section.