Search and Rescue Insurance?

On an previous thread the question of getting comprehensive travel insurance for an extended trip to Nepal came up. As nobody came up with an answer I am asking this as a separate question.

Various websites say that you need Search and Rescue cover for trekking. The only (UK) policy that I have found that specifically covers Search and Rescue is through the British Mountaineering Council - other insurers say they will cover the cost of a medical evacuation by helicopter but not the search or non-medical evacuation. That would be ok but we we also want to do some rafting while we are in Nepal and that - according to the BMC insurers - puts it into the Alpine & Ski category and adds 50% to the cost : ((

Any suggestions anybody? Is it possible to buy extra cover in Nepal - either for the rafting or the S&R?