Sadly I suspect you'll find the old adage is true: you can only get insurance when you don't need it. For when you need it, you can't get it. I hope this isn't how it turns out for you though.
Lloyd's Cox's and King's must be a possibility.
Another useful source of advice would be the Forces Pension Society, which
everyone serving and ex of all 3 Services should join as a matter of principle. It's the ForPen (formerly the Officers Pension Society) who fought the War Widows' campaign and many others of good, sensible and worthy cause.
http://www.forpen.co.uk/banner_and_navbar.htm
Sign up guys!