Just noticed your post!
In the Lowveld (Slowveld) Mpumalanga there is an abandoned mining village called Masauli (26 00'15.88"S 31 04'33.19"E). Check it out on Google Earth.
Best approach is from Barberton, if you approach from Badplaas, it's a nightmare with road construction. The asbestos mine was shut down a few years ago and now the village is empty. There is a boom gate at the only two entrance points, no problem with the guards just say you passing through.
The village is maintained, so it's not quite like Kolmanskop but a short walk around is crazy, empty school, rec club, golf course, clinic etc.
There are several great off road routes around the Nelspruit/Barberton/Swazi boarder area shout if you need some help.
Redshift3