Cape Corps
58 Cape Corps are listed on the Jerusalem CWGC memorial
South African Mounted Rifles
5 Mounted Battery, Central African Imperial Service Contingent, Nyasaland
JG Maker diary part 1
JG Maker diary part 2
South African Hospital, Richmond
South Africa Remembers (Margaret Frood)
While not a WW1 unit, many who served in World War 1 had links with the 1899-1902 South African or Anglo-Boer War. These links might be helpful in tracing individual records.
Casus Belli (pay to access)
Index of the Regiments and Corps of South Africa has summary information on South African units pre and post World War 1.