This is every man's nightmare, and the reason I want to put a live satellite tracker in my Morgan (running a TR4 engine)
By your description below, sounds like a nice car. May be worth finger printing the bike and have them run by your police to find out who this is.
If you had a key hidden in the car, it's likely you know the thief.
Otherwise search Ebay and Craigs List for parts that you know are unigue to your car, or spitfire model parts by seller in your area (couldn't have come from too far, being on a bike)
Brad P