As far as I'm aware, the access to the Groblerz boulders was lost when the farm was sold (a couple years back). I can't remember the directions there anymore
I only went there once.
The bouldering was sharp but okay. As far as I'm aware Sean Cremen and James Roberts did most of the development. I 'think' James had a guide for the area.
However access would obviously have to be arranged before, perhaps you could put in some leg work since you live in the area?
I'll try to have a look to see if I can find the area on Google. Maybe Andrew can help you out, but I'm not sure...