Good question, Y'know google did not provide a easy list of SA currency thickness.
Google tells me A dime is 1.35mm and a SA R2 is 1.83, a SA R1 is 1.09mm and a 90's 0.0 1c was 2mm. That's all I could find.
So something slimmer than a R2 and thicker than a R1 - maybe . 20c or 50c? Or just use a 1.3mm plectrum :grin'