Your best bet is the Cornwall TRF forum, see if someone can take you out is even better. Personally after last weeks run in Cornwall, I wouldn't like to take a wrong approach to some of those lanes
Down at end of May staying at Mullion not sure I would call that mid Cornwall. How far away are you? Will post something on the forum closer to the time and thanks for the offer. Thanks to everyone else for their comments not used to talking about trail riding on these forums the TRF has opened up a whole new side to trail riding didn't realize how many like minded people there were out there