The most common way nonprofits get insurance is by working through licensed independent brokers. Brokers help nonprofits determine the types of coverages they may need, and can shop the market and get them quotes for those coverages.
Brokers are paid a commission by the insurance company to service the account for their nonprofit client. Though not common, some brokers charge a fee to service the policy for the nonprofit in addition to receiving a commission.
One broker can provide you with quotes from multiple insurance carriers. Presented with the same information on the application for insurance, the price of insurance should not vary depending on which broker requested the quote.
More important than location is a broker who is knowledgeable about nonprofit insurance, has attention to detail, and who responds in a timely manner to emails and phone calls. A good broker who specializes in working with nonprofits can provide nonprofits with a high level of service and knowledge of the nonprofit marketplace - regardless of where they are located!