This is the only Cornish speaker I know of on italki:

https://www.italki.com/user/2462420

He isn't offering lessons - but if you contact him, he may be able to help you out.

Hi Luke. 

Celtic languages are not so popular so I think it will be a real challenge to find someone who can help you - espercially with Cornish, Manx or Breton. I think that you should check the Language Partners section.