I have the parts catalogs from 3 nearby dealers, 2 of which are Thor dealers, and can generally find what I need in the catalogs. The catalog will give me the part manufacturer's name and part number, as well as dealer part number. I then take that info to google and find what I need on-line.
I've been doing this for a few years and usually find what I need at a reduced cost.
Unless you are dealing with color or trim specific items most parts cross lines between manufacturers and models.
US Army (Ret)
2020 Entegra Accolade 37TS
2019 Jeep Grand Cherokee Trailhawk (Toad)
FMCA - F432054