Welcome!
Maybe a few, but we're mostly based in and around Victoria. I think the AUF Spearfishing club for SA is
http://www.freediveextreme.org/ABOUT_US.html (though there might be more).
Having said that, both Ewans and Port Macdonnel are very much worth a trip. Robe as well if you're on the way back to radelaide. (Port Macdonnel and Robe for crays
Clearest waters I've ever seen was at Ewans. 80+ meters of viz. If its a clear calm night, you dive down to the bottom of Ewans and sit on your back and you can see the stars through the water. Its pretty amazing.