Where can I find out about RV-only listings with a "Buy Now" option, specifically in California?

Combine the vehicle-type filter (RV/Motorhome) with the "Buy Now" listing-type filter and a California location filter to narrow results to exactly that combination. If results are limited at any given time, RV inventory tends to fluctuate more than standard car listings, so checking back periodically will surface new units as they're added.