I can find no record of the marriage in South Australia or Victoria (using the Pioneer Indexes) and there is no sign of an Australian marriage in the Australian BMDs on Ancestry. George was a mariner and seems to have got around quite a bit with some information on Ancestry suggesting some time spent in New Zealand as well as having been in NSW, South Australia, Victoria and then Western Australia.
And there is still that rather large gap between the stated marriage (1863) and the first known child in 1879. And the subject of children does pose an interesting question regarding the marriage. I've just checked the indexes again and found the following probable births:-
South Australia
William Henry BRISTOW born 1879 Port Adelaide - parents George and Elizabeth (OATES)
Charles Robert BRISTOW born 1880 Athelstone - parents George Robert Read and Elizabeth
Beatrice Louisa BRISTOW born 1881 Port Adelaide - parents George and Elizabeth (OATES)
Victoria
Winnifred Victoria BRISTOW born 1885 Fitzroy - parents George and Elizabeth Ann (OATES)
Joseph Bannister BRISTOW born 1887 Fitzroy - parents George and Elizabeth A (OATES)
New South Wales
John George BRISTOW born 1883 Redfern - parents George and Elizabeth
Lizzie BRISTOW born 1885 Sydney - parents George and Lizzie
Richard A BRISTOW born 1892 Sydney - parents George and Elizabeth A
It will make it a little easier to follow if I put them all in chronological order:-
1879 - William Henry born Port Adelaide, SA
1880 - Charles Robert born Athelstone, SA
1881 - Beatrice Louisa born Port Adelaide, SA
1883 - John George born Redfern, NSW
1885 - Lizzie born Sydney, NSW
1885 - Winnifred Victoria born Fitzroy, Vic
1887 - Joseph Bannister born Fitzroy, Vic
1892 - Richard A born 1892 Sydney, NSW
Assuming that all children do indeed belong to the same family I would deduce that Elizabeth was probably born no earlier than 1843/4 given she would have been age 48 or 49 when Richard was born in 1892. Women were certainly having children up to age 48 during the 19th Century but I don't think I have ever seen an instance where the age exceeded 49.
That suggests a marriage in 1863 would certainly be in order but I have to comment again on that 16-year gap before there is any evidence of children.
After checking the Ancestry family trees again and then checking the South Australian records it does appear there could be one more child:-
Mary BRISTOW died 25th July 1880 Glanville, SA age 2 - daughter of George Bristow
No birth record can be found for Mary in Australia and no children were born in New Zealand.
Not quite sure where to look next on this one.
CT