If you rent through a broker or a dealer, they will find the coverage you need to have, and the providers for coverage each renter needs to buy.
Some of these insurance companies will not deal with you as a private individual, you may need to have status as a rental business to find the coverage you need, depending on what state and how insurers are regulated.
What this insurance costs may shock you. For a single vehicle it will be much higher than the cost to insure for personal private use. Brokers and dealers might buy insurance for X number of vehicles at N total valuation, the umbrella their liability for the fleet. Thus not everything is fully covered but there is coverage enough for what is at risk at any time.