Family tree research in Africa in 1800's.

My Great Great Great Grandfather was a black African man born in the Cape of Good Hope, Africa in 1835.  His surname was Cumis or Cummis and his first name was Sims or Symns.  He also used the first name William.  He was English illiterate and so there are many different spellings of his name/s, including Comas, Comes, Cummas, Cumas even Cumins,

Can anyone tell me how to research his family in Africa?

 He was a miner in the Bendigo area of Victoria in the 1860's and 1870's.  We know he lived in Maryborough and Chewton, and spent time in the Castlemaine Hospital. Apart from the period of time when he married and fathered children he is a mystery. We can find no records of his entry to Australia.  Nor can we find any death records.

Not sure how to even begin researching his African birth records.
HELP!
Historically yours,
Valerius Copernicus.