Yes, I hear Wlaker do some very nice work.
First thing to do is work out exactly what you want the cage for, and what regs it needs to meet (ANDRA, CAMS etc) get a copy of the regs to be safe.
Then you can work out where to go.
Also, if your car is a streeter, be aware of the rules for cages in road cars in SA.
Here's an extract of the rules for vehicle modifications, although it may be an out of date version - hope it helps you.
Basically a cage that meets CAMS or ANDRA regs will make your car illegal in SA.