Welcome the world of much loved senior coaches.
Fortunately, you will find that there are very few manufacturer specific parts in the coach itself. Remember that the coach and the chassis were separate parts put together at HR. Most of the coach parts are still available. For those that are not, there are usually suitable replacements available. As an example, most of the light fixtures in our favorite coach were plastic and have died of the old plastic disease. I just found others to put in the place. This is continuing as I write because I am also changing many that we use most to LED. If it doesn't cover the hold, use something to cover the hole and the mount the new piece to the hole cover.
There are HR groups on other forums.
Word Of Advice (Free advice is often not worth the price) ...
Get all the service documentation and parts lists for the chassis and all the components that you can. You many be able to download many from the web, you may have to buy some and they will seem expensive - until you need them. If you have those onboard and something needs work that you can't do, you can very possibly find a wrench that can read and he may be able to get you going again. Don't even count on finding an RV shop that knows about your rig.
Matt
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.