Hi Wildrice,
We missed you at the Vous this year.
I know that TCJapan had a wooden tree made for this type of occasion a few years back. I also heard from a few of the Japanese that it was the scariest tree they had ever climbed. If you do a google search you may be able to find some pictures. It is also featured in one of John Gathrights tree climbing books.
Another source that I know of produces metal tree's. To me this seems a bit more sound.
http://www.thwaites-services.co.uk/innovation.html
Best in '09