In Woodmead (N. Joburg) you will have the big store Makro. There you can buy GPS.
I remember another Makro on the road from the airport toward the city.
I should have added - to be sure it's loaded with the software for South Africa. If you have to buy that separately, it's expensive. If you could beg, borrow a Garmin GPS there in Canada, you could buy the software directly from Garmin for $100.
We spent 3 weeks driving SA. We purchased a new GPS at home and the Southern Africa maps on-line. If you buy at home or purchase locally always have backup paper directions. There were several situations where the GPS knew the hotel, but then took us on a parallel road near-by causing us to backtrack for miles. We arrived frustrated only to hear that this was a known problem that the hotel owner had been trying to get corrected for some time. So use the GPS for general directions, but have a second source of directions outside of the largest cities.
There is also one (Germinston)
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