Brian,
If this is your first visit to a Prevost facility ask for a tour. In terms of excitement there won’t be much, but you will see a lot of coaches getting worked on. It will make it clear in your mind just how much expertise is at the service centers.
The parts department is a candy store for Prevost owners. If you need it or want it they got it. They have large inventories because each of the service centers parts departments not only supply parts to the shop, they also fill orders around the country. It is likely if you need a part at your home base, and the nearest service center does not have the part in stock, another service center will be shipping it to you. Remember these guys take pride in their role in keeping commercial buses on the road so the parts guys are doing what it takes to get you your parts.
I cannot answer what it takes to set up an account. I have an account, but I have had it so long I no longer remember when I got it, or how I got it. I do know that ordering parts when you have an account is as simple as pie. Your vintage coach may be tough to get parts for on those parts that are not common with later model coaches but so far I haven’t heard of anyone that couldn’t get what they needed. Some parts just took longer.
I do strongly recommend that you shop non Prevost parts through truck parts supply houses. Prevost is excellent on some parts on pricing such as on air bags, but there are some items they are not competitive on such as some generic brake chambers. I always give them an opportunity to quote however. When they run specials nobody can touch their prices. I bought my last windshields for $133 for example.