As one who does mechanical inspections on motorhomes, I believe your desire for a "buyer's agent" is flawed.
At least in the normal use of the term-- a salesperson working for the buyer. They would only get paid if you buy. Hence the more time they take showing you coaches, the more that are "close, but not purchased" the less money they make in a year of doing that.
My recommendation is to start shopping-- start ruling in/out coaches and make a short list. Then ask specific questions here or on one of the other on-line RV forums.
Choose a coach or coaches that meet your needs. Locate a specific coach that you like. Make an offer "contingent on inspection and test drive". If you are not familiar with both the chassis and house systems, find someone (a neutral 3rd party) who is to go over the coach WITH YOU (so your eyes see what their eyes see-- lots better than a written report).
Renegotiate deal if deficiencies.