Nicola, there are three more two seaters in the UK - I don't know how they are fixed for giving joy rides - they are owned by Historic Flying at Duxford, Anthony Hodgson / Dragon Flight in North Wales, and Maurice Bayliss which I thik is based at East Kirby in Lincolnshire. Bit of Googling might find you the contact details. Good luck with it, wish I had a wife (or daughter) who'd buy me a ride in a Spitfire!
Cheers
Treadders