for events like this and racing are much different than in the UK. There is a co. that offers DE insurance, but it's not widespread across all 50 yet. There is also racing insurance for on-track exposures, but it does not apply to amateur racing.
There is a guy out of Canada that has been selling DE insurance for a few years. It has recently been determined by several state's Insurance Fraud Investigation Divisions that this is not a valid co. nor is it insurance. The person in question has been accepting premiums from clients and in return self-insuring these people and their equipment. This is illegal and is considered a federal offense. This individual currently has a US warrant out for his arrest. Please avoid contact with anyone selling this type of insurance out of Canada.