I'm sorry for your problem, but really, what you are asking for is not insurance but a charity. Why would an insurer want to take you on, KNOWING that your drug costs would far exceed your premiums? I'm no big fan of the med insurance business, but I think that i am on their side in this case.
Looks to me like you will have to maintain access to the tax supported national health
system... and be damn glad to have it! We have had to return to the USA for serious medical
issues since MEdicare does not cover one whilst out of the country.
One of the aspects of cruising that they don't tell you about at the boat show!