Have a look at backpackers insurance or mountaineering and trekking insurance policies.
We used a backpackers insurance for our DD when she was doing martial arts as it covers many 'extreme' sports.
Thanks dally - found one
Was 5 few years ago now, but our DD climbed Kilimanjaro. At the time we got cover from AXA Middle East.
It was called Now Health International.
I would also check your own insurance as you may be covered and sometimes just have to pay a little bit more on top to get cover.
Thanks very much for the info