knottinbotswana

That's a South African registration plate, specifically Gauteng Province (GP) which covers the conurbation of Pretoria and Johannesburg. Edit to add: Reverse image search suggests it is in Bellville, Cape Town which is home to a large Transnet (national railways) yard. SA Transport: https://www.sa-transport.co.za/trains/rail_vehicles/rail_veh.html Location link: https://goo.gl/maps/TQGXiQpTGYzB7bNf9

I can't help with timetables or specifics, but the author Martin Meredith has written extensively on this era, I recall snippets about goods and materiel in the text so there may be links to sources in the bibliographies. Not sure about your friend's contacts in RSA, but would suggest looking at some of the South African model railways groups and model shops. A short list http://www.northstarrailway.com/model-railway-clubs/ albeit some of the links are dead, but you/your friend may find the successors on Facebook. I have also been to https://modeltrainshop.co.za/ where the owner may have some knowledge. Good luck: I have the pleasure of living a little further north in the region, and can fully appreciate the difference made by having access to rails and steam engines rather than relying on horse and oxen.