Hello! I, too, am amazed every time I see the adventure playground in Berkeley! I've never tried to do anything myself, but I found a couple of resources out there and I would LOVE to explore the posibility. I'd start with http://adventureplaygrounds.hampshire.edu/index.html , a good cover of why it's a good idea (in case you need to explain your dream to people you contact); also, check out the Project for Public Spaces at www.pps.org -- there are lots of other "adventure playgrounds" in the country and there may be one close to you that you can check out.. maybe even meet other similarly-minded people! Do come back and keep us updated, and good luck!
Cheers,
Aron