Hi Loopy
Yes, I had entertained the idea that John Cameron was not born in Scotland. Accordingly, I examined the GRO.gov.uk birth index in depth with all variations of mother's surname. There are no births to a mother Graham or Green. The births in Dec Qtr 1864 and Jan Qtr 1865 have mothers' surnames included, so no joy in England.
I also did do a search of the Irish civil registration births and again no joy there.
I have also searched for the marriage of the suspected parents in England and in Ireland. No luck on these. Unfortunately, there's not much point in searching for death certificates in England or Ireland as neither provide sufficient identifying information when the place of residence is unknown.
As to the marriage certificate for John Cameron and Catherine Campbell, the details are:
1889. Marriages in the District of Bothwell, in the County of Lanark.
p. 47, Entry #94
1889 on the twenty-seventh day of October at The Episcopal Church Uddingston after Publication According to the Forms of the Episcopal Church in Scotland
Groom: (Signed) John Cameron, Coal Miner (Bachelor), 35 years old, residing at 57 Single Row, Aitkenhead, parents Joseph Cameron General Labourer (Deceased), Sarah Cameron M.S. Graham (Deceased)
Bride: (Signed) Catherine Campbell, Domestic Servant (Spinster), 27 years old, residing at 24 Double Row Aitkenhead, parents David Campbell, Coal Miner, Mary Campbell M.S. Ford
Witnesses: (Signed) Henry Bruce, Rector of St. Andrews Uddingston; (signed) David Campbell witness; Maggie Swinburn witness.
Registered: 1899 October 28th at Bothwell. William McNab, Registrar.
David Campbell was either Catherine's father or her brother. I have no idea who Maggie Swinburn was. She did not marry any of Catherine Campbell's brothers.
I hope this information helps.