Not highly reliable and not the web (which can be just not as good as in person upfront) but worth a try : go to the library and go through the local papers, make sure you pick up those free papers around town (Big Nickel, Dandy Dime, name depends on your area), also check any bulletin boards that let people post items for sale, possibly radio call in shows buy/sell, I have also had people come to the door and ask if our trailer/pop-up/motorhome might be for sale. The local RV park let's people post RVs for sale on their bulletin board and sometimes has them out front.
I live in the boonies so my way of doing things might not work for others. I think that "RV wanted" is useful because some people, and I don't blame them, don't like going through advertising, fielding calls and putting up with people that like to come just to look or make a steal of a deal.
Good luck in your search.