Did they say they don't have a map?
Most cemeteries are divided up into sections so a grave number might be e.g. 482 M - meaning grave 482 in the M section. The precise position of one grave with no headstone is not always easy to find but if you have the section number, can be shown where that is on arrival (if not obvious), if there is a stone you can just walk through until you find it.
Assuming there is a known section, a stone and its not under a mass of brambles, of course.
Bernard