cresby.com links to Folknews Kernow which was THE listing site for Cornwall.

Looks to be a year out of date and no lists.

Wadebridge FF
Cornish Music

a links page you might find rewarding click one of the links it has what you want. But there are others.

Failing that I can put you in touch with Heather Dale - a Canadian who comes over every year and specialises in Cornish Songs and festivals in Cornwall. She might know.