This is a brick wall which I just can't climb or knock down!

John BOWDEN b. 1 Jan 1783 Constantine m. Mary MOYLE. John d. 26 May 1830 Wendron, I have no death/burial for his wife, Mary and I can't find her in any of the Censuses.

One of their sons was John BOWDEN b. 23 July 1815 Wendron who married Eliza Unknown. From the following transcription on a gravestone in Constantine, I have deduced that Eliza was b. 1826, she died 8 June 1861 and their son, William BOWDEN was b. April 1861.

I can't find any of the above three people in any of the Cornwall Censuses either! Surely they've not been missed from three of them (1841-1861)?

Does anybody have any ideas? How can I find out the marriage date of John and Eliza?

Gravestone Transcription:

SACRED TO THE MEMORY OF

ELIZA,

Wife of JOHN BOWDEN of this Parish
Who Died June 8th 1861 aged 35 YEARS.

Also

WILLIAM,
Son of the Above
Who Died July 26th 1861 aged 3 MONTHS.