AFAIK it's Truro MC that covers the whole of Cornwall. No idea if there are any 7.5 tonne lorries based at any DO in Cornwall (my gut feeling is that they're probably all based at Truro MC). Nearest distribution centre is off in Bristol.
Address: St Ives Delivery Office, Penbeagle Industrial Estate, St Ives, Saint Ives TR26 2XX
Phone: 01736 795923
Might be worth calling them and having a chat with the DOM there. If the DOM there doesn't know, they might be able to point you in the direction of someone that does know