Ja as far as I know wildcards do work in rocklands.
you can get a wild card for the specific province you are in, I think for the Western Cape it's about R170 or you can get a national card (about R250). These cards do allow you free access into any (governt not private) of the nature reserves and game parks in the specified specified, for 12 months from date of purchase.
So if you had a national card you would have free access to the kruger park as well as silvermine
Please don't qoute any of the prices I have stated.
I think it is best to get hold of nature con in your area.... but be warned they are probably gonna send you all the way around you province from one department to the next... only to get help where you originally started.
it's the same story with any government run establishment... Good Luck