Oz2, try the following operators, they all operate UN/Red Cross contracts from time to time. You should be able to get a C208 rating at Lanseria Airport (Johannesburg) or otherwise Fedair in Durban used to do them. Better option is to get the rating on your national license before coming over, as it will make conversion/validation to SA license a lot easier.
www.airserv.org
www.naturelink.co.za
www.norseair.co.za
http://www.kingair.co.za/
www.solenta.com
www.fedair.com
www.safair.co.za
http://www.qwila-air.co.za/
http://www.zimex.com
http://www.transafrik.com
http://www.swiftair.com/actividades....vo=act_charter
Forget the politics and enjoy the experience, it is some of the best flying you will ever do. Good luck