Having done a fair amount of research on this earlier this year, I can offer three perspectives that might help clarify things for you.....
1. If you are doing a high-speed event, like High Performance Drivers Education (HPDE), go use the link for On-Track that Venomiss posted earlier in this thread, or alternately, use this one from Lockton Affinity
HPDE Insurance Program . While these are Damage policies, and not Liability, I have personally used Lockton for track events with Corvettes, Porsches, etc. and I think that you'll find their coverage to be good, and reasonably priced, given how difficult it is to find these days. I know that in the case of Lockton, it was created
by track-rats,
for track-rats. One hitch is that they don't cover all events - it's on a event-by-event basis, with the event sponsors pre-qualifying through a process with Lockton to show that they run responsible events.
2. If you are doing an auto-cross event however, Lockton will not cover you (and I'm not sure about On-Track). This is because it is timed, which is one widely accepted definition of racing (which is taboo in insurance circles). However, most auto-cross events have a fun-class, which is by definition not formal or sponsored racing, so you may have some luck with your insurance company with this approach. On the up-side, auto-cross is much, much lower risk than HPDE, so most folks don't bother with insurance. However, having said that, I have heard stories about parked cars being wiped out at auto-cross events because some numbskull went WFO off the course.....
3. If your VCA club is sponsoring the HPDE or auto-cross event, then they need to get Liability insurance to cover
the club for the event, and that is available through national. They have an arrangement with K&K, I believe.
So, the bottom-line is that you probably won't find Liability coverage for auto-cross. But, do you really need it?
Hope that helps!