I had to renew earlier this year and reviewed the Red SA Air Law book that I picked up at the FBO where I did my renewal.
The test was straightforward and I did not feel I needed anything more than the Air Law booklet.
Edited to add:
If it is just private you are looking for, the book is
South African Air Law for Private Pilots - Lilith A Seals
The link below also has another book Air Law for South African Pilots.
Both ~ ZAR 150.
http://www.cometaviationsupplies.co.za