Felix
Try these people
competition car insurance Alot of the racers with Bemsee use them. I got £16000 cover for 2 race bikes, wheels, spares, £2k worth of tools and it was about £368 for the year.
You're bike is covered for fire, theft and accidental damage whilst in storage i.e. your garage, during transportation to and from circuit and at the circuit...but not when the engine is running and on the track.