Hi Ian
Do you perhaps have sibling or parent information? I've scanned a few sources (outline below).
I've gone through the SAG series, and:
- Vol1 (A-C) Couldn't find any records for John Charles (also looked at alternate spelling for Bowes)
- Vol 12 (So-Sz) Couldn't find any records related to John Charles, Lily Steenkamp, or Lillian Steenkamp
In the book "Steenkamps van Suider Africa" there are also no usable traces for John, John Charles, Lillian, or Lily.
www.gendatabase.com is a good record database for South African records. Under the following sections I couldn't find any related information:
- Deceased Search
- Marriage Search
- Spousal Link
- Estate Search
- Immigration Search
Hope this at least eliminates some sources from your search, or guides with new info :)