If you could get hold of Berkovitch's book "The Cape Gunsmith" (published by the Stellenbosch Museum in the 1970s) you might find information. The book was accessible on Google Books after a lawsuit by several publishing houses forced Google to withdraw it from the website. I seriously doubt that there are any copyrights, though, and, perhaps, one of our South African members with an entrepreneurial bent might want to bring out a limited coffee table edition.

Hope this helps.