Act as a customer - I work on the medical insurance side and frequently interface with large insurance broker and consultant groups trying to gain visibility of our product so they sell it. Some of the larger brokers are Mercer and WTW. Have you considered working for one of them for a while to see how they generate leads? It seems most of them have a formulaic approach for generating leads and work closely with insurance companies to ensure the product they sell is what employers want. You could also act as if you are a customer trying to buy insurance and see how existing brokers connect with you, ie online, networking, conferences.