A Club can get insurance through the NMLRA. Some clubs and the rendevous system host events on private land all the time. One of the local clubs here, is only on private land owned by another and they have been there for at least 25 years.
I looked into running a BPCR match years ago, and the jerks at a national organization (Not the NMLRA) wanted us to (1) have an incorporated organization (non-profit or not for profit ok) and (2) pay an assciation fee of about $200 before we could be considered as eligible for the associations's group insurance. We couldn't get them to tell us if the insurance was $50 a year per event or $5,000 a year per event. That information couldn't be released to non-member orgs.
I called an insurance agent who write insurance for "shooter" farms and hunting camps. Basically, he suggested a single event type of insurance, which wasn't cheap. IIRC it would have been a little over $300 for $1,000,000 coverage for everyone involved inculding the land owner.
I work with auto insurance policies and dealing with trying to get insurance for a BPCR event was frustrating to the point that we dropped it..