Plasma nailed it, I had a race car coverred in this manner, the only time it was NOT covered was while it was in competition.
Try also K&K insurance and Haggerty

BTW, recently there was a wreck at an autocross event in Ca, most cars for auto-x are street driven cars and the race is against the clock, but... since it was "competition" and a stuck throttle took out 3 parked cars which were "enterred" in the event, the insurance DID NOT cover them. So read the fine print.