I visited the old part of Harelaw last Easter and although it was a little overgrown had no problem in going round it and inspecting most of the graves. I didn't have time to go up to the newer part which looked very large, and, from a distance at least, in reasonable condition. However, had you considered starting by getting the microfilms of the Harelaw and Collierley Burial Registers via your local Family History Centre? They are on films 2104606 and 2104607, and apparently run from 1891 to 1998.
JenB