I know we used to be able to get them from the National Geo-spatial Information in Mowbray in Cape Town. You would need the map sheet reference number and they would put them on a flash card for you. Not sure how it works these days, looks like that is now sitting under the Department of Rural Development and Land reform who have offices in Pretoria. You could try them, though they are more likely to give you a file than print something. Could then take to a print shop. There website seems pretty messy and broken though.
Last I played with Avenza maps also had SA 1:50k topos. Could either use that to find the reference (Looks like it is 2430AA SERALA) or possibly print/download.
If nothing is working out the CDNGI data portal is pretty useful. You can set it to NGI Topo in the top right then start turning on the layers you want, has a local print function just set it to 150 dpi and the scale you want.