Hi there
The IGI does have the marriage of John Fish to Fanny Bunn on 27 April 1812 at South Elmham, St Nicholas.
This is a submitted record, not a controlled extraction, so caution is advised. However the details are remarkably precise so they may be correct.
Also there is another submitted record indicating that Frances (Fanny) was baptised on 21 Sept 1794 and that she was the daughter of Joseph Bunn and Elizabeth Allcock.
Dave