Right, just spoken to the visitor center and here is the latest on the Triumph Tour availability. I explained that you were making a whirlwind trip back to the UK for family reasons(?) and details below:
They have a full visitor center which is free of charge spread over 2 floors with a full history of Triumph motorcycles and various models on display. The only date they could squeeze you in would be on Sunday May 6th. Closed Monday and Tuesday, and your date of the 10th is private parties booked for the whole day, likewise for the 11th - 13th. If this is any use, I can call and book tickets which will need to be collected on the door. Tours are timed, so you might get an AM or a PM tour. Any use???