Keith, there has been a lot of discussion about insurance over on STS, the Searey Technical Site. (To join STS, just click on "Help" at the upper right of this page and enter your name, contact info, and Searey kit or serial number. And mention that you'd like to join STS. In a day or so you should get email telling you how to log in. If you have any trouble with that, let me know and I'll help you.)
Briefly here: I'm older than you and still have insurance--but it has been harder to get every year since I hit 75. It's clearly age-discrimination. My broker is Falcon, the Seaplane Pilots Association's broker. Several other Searey pilots have recommended other brokers. Search for "insurance" on STS for them. And Avemco has been a last resort for several pilots--a last resort because they don't seem interested in insuring passengers.