Yes Ross,
I have some idea...
My coach came with 8.75x16.5 and they are not easy to find as the only US manufacturer is Firestone. Many are already old on the shelf.
After some searching, I was able to find rims with the correct hub center diameter, bolt circle, offset and shape (required to clear the brakes) that are 16" and the same width. I suggest that you collect at least those dimentsions and start hunting. It will help you a lot if you know who made the chassis of your coach. The wheels you want are pretty common in agrarian areas (Not East MA). You may be able to get them from Southwest Wheel, but the the shipping will be a big issue.
If you do find 8.00R16.5 read the date code before you pay for them. Tires only last about seven years on the shelf on the road.
Matt