Any South Africans here might find the following useful....
I get my Arduino stuff from MicroRobotics in Centurion.
Pure electronics stuff from Mantech in Johannesburg, who incidentally bought Pons. (Not that there was much left after their building burned down.....)
I found Screwman in Pretoria CBD great for things not available in normal hardware shops, like standoffs and rivnuts.
Rothmar in Wynberg (Sandton) are good for bearings, and can source cheaper brands if huge loads are not a requirement. No website but email Paddy
Lastly, Piet Els at Priority Solutions for laser cuttting of plastic and wood.