Have you called (or visited, or emailed) the local public library and asked the reference librarian? I worked at a community archives (my very first archives job!) and we essentially had an index of all the graveyards in town. Helping people research the history of their property is something local history archives and local libraries do a lot though! There's a few different methods, usually in my area we started with plat books but it was a farming area in the Midwest, I'm not sure about your area. But your local public library is a good place to start, they'll point you at the right local resources.