There is a Guild of South African Luthiers, founded in 2000. Most of them work on guitars, some do however build ukuleles as well - Rob 'The Guitar Doctor' Drake in Capetown comes to mind.
Part of the abscence of ukuleles in the Southern part of Africa is because of the presence of a direct competitor, the ramkie (in Afrikaans 'blik kitaar', in Setswana 'katara', in Zulu 'igogogo'). It's the size of a ukulele, but box-shaped and tuned to an open chord, often open F (cfac) or open C (gceg), in a linear way (which is odd, because a lot of African music guitars have some sort of re-entrant tuning). It's quite a bit older than the ukulele, Saartjie Baartman (at the time forced to perform as the Hottentot Venus) played one from 1810 on. Some claim it's a primitive copy of the machete (Percival R. Kirby makes that point), others see similarities to banjo-like instruments from Central Africa (David Rycroft), one early 18th century source even claimed it was a copy of an Indian instrument (O.F. Mentzel). The way of playing was very similar to that of the machete: intricate chord-strumming, rather than playing melody.
Since ramkies are considered folk instruments, often made out of scrap material (tins, boxes, brake wire) they are made and sold everywhere but you have to search for playable ones.