I came across your posting while I was trying to check some facts about John Mitchell de Kretser. If you are still looking for information, I may be able to help.
My husband's family had some papers that show he is a direct descendent of John Mitchell de Kretser and we have a photograph of him and his wife Henrietta Emelia Raffel taken around 1900 in Colombo.
I have been building a family tree on another site and as I was doing that, I realized that there is an anomaly about John that I would like to clear up. The papers we have are a typewritten transcript of an extract from the Journal of the Dutch Burgher Union of Ceylon, Vol. XLVII No 4, October 1957 which states that John Mitchell de Kretser was baptised (not born) on 3rd November 1833. However, it also shows that he had an elder brother John George Michael born 10th June 1832. Although I have seen 2 family trees that show it was John George who was married to Henrietta, I am inclined to think that he actually died in infancy, which is perhaps why the next son was also named John, but it would be good to have proof of that.
Anyway, if I can give you any further information, please let me know.