From the CAMS site, here are the clubs which regularly do events:
BOLWELL CAR CLUB OF AUSTRALIA (SA) BRANCH INC. KENT TOWN SA
EP AUTOSPORTS CLUB INCORPORATED CUMMINS SA
FERRARI CLUB AUSTRALIA INC.SA STATE COMMITTEE BELAIR SA
FPV & XR CAR CLUB SA INC INGLE FARM SA
IMPREZA WRX OWNERS CLUB SA INC. MAGILL SA
MG CAR CLUB OF SA BROMPTON SA
MILLICENT SAND BUGGY CLUB MT GAMBIER SA
MINI CLUB OF SA INC BLACKWOOD SA
MITSUBISHI GSR/EVO CLUB MODBURY SA
MODIFIED MINI CAR CLUB OF SA INC. MARDEN SA
NISSAN DATSUN CAR CLUB OF SA PROSPECT SA
PORSCHE CLUB OF SA KENT TOWN SA
SOUTH EASTERN AUTO CLUB OF SA MT GAMBIER SA
SOUTHERN DISTRICTS CAR CLUB
If you want info on how to contact them visit http://www.cams.com.au and click on the clubs link. If you speak to them they should have a full list of what's on.
You don't need a helmet in NSW unless you're in an open wheeler. Assume it would be the same in SA.
I'd definitey recommend giving it a go- khanas are heaps of fun and a cheap way to get into motorsport