I don't think the venue matters. I use Hallmark Horse (mortality and major medical) and they have been great to work with. If you do a search on insurance here you should come up with quite a few threads.
Quite a few people in my barn use them. They seem to be quite nice to work with. They are based locally. They sponsor/support a lot of horse-related endeavors which I always like to see. Donna rides HJ and shows. They gave a pretty good quote to one of my barnmates.