Hi Rick,
It depends on what sort of quantities you are after. From my experience so far there aren't wholesalers in SA but you would be able to purchase blanks from a reseller. Pretty much any screenprinter or promotional products company would be able to help you out. If you have a reasonable order it may be worth sourcing from Melbourne or Sydney.
Try Gildan, LW Reid, Johnny Bobbin, Ramo, AS Colour just for a start. Not necessarily in that order. Check out some of the threads in the Aussie section on this forum for more info on particular suppliers.