They have baptisms and burials for St Mary Abbots 1813-1845 here on Ancestry in the London parish records
In the burials, in all those years, there are only three for Corbett (can't see any spelling variants at the moment either)
16 April 1829, Henry Corbett, abode Pembroke Square, age 1 year and 6 months
19 June 1829, Elizabeth Corbett, abode Kensington Buildings, age 41
18 May 1838, John Corbett, from the Workhouse, age 44
It almost looks from this and the few baptisms with the name, that your John + Elizabeth could have been among only a few people called Corbett or Corbut who were around in the parish of St Mary Abbots.
And there are always likely to be spelling variations in these parish registers, so it's possible John's parents (possibly a brother too) were already dead by 1841?
There is a death certificate for John Corbett, June 1838, Kensington, 3/224.
May not be him of course, and they may have moved somewhere nearby perhaps, but does look possible that its them.
Do you know when John and Elizabeth married?