The marriage record is on rootsireland.ie/ but doesn't have much info!:
Date of Marriage:14-Feb-1819
Parish / District:CASTLETOWNROCHE
The Irish Census of 1821 (free online) doesn't have Cork records!
The Tithe Applotments (free online titheapplotmentbooks.nationalarchives.ie/ which have 342 Roches in Cork but only this one in Castletown
www.irishgenealogy.ie/ (select church records) is good for Cork records if you haven't already tried there.
I suspect you've tried there but the Natnl Library has the R C registers free to search and has Castletownroche baptisms & marriages from 1811
Was Castletownroche named after the Roches I wonder?