Are you aware Parish Registers for Cornwall are available on FamilySearch ?
https://www.familysearch.org/search/collection/1769414
To see a list of all Parishes available click on the "Browse all 202,325 Images". Gwennap appears to have the relevant records for that time period.
There is the England Project and they have county teams. The Cornwall team is here. The Cornwall team has a resources page which talks about some of the places to find sources.
If you want to search and create citations for the Cornwall OPC the WikiTree Sourcer extension will help you with that.