I feel like if you can't find one that is rated high enough then get the highest rated one. It will have a better chance of stopping a fall than no harness.

also check this ( http://www.google.com/search?sourceid=navclient&aq=t&ie=UTF-8&rlz=1T4TSHB_en___US208&q=fall+arrest+sys tems) you may be able to find a system designed for another application that can be adapted to the woods.