at Sportsmansguide:

http://www.sportsmansguide.com/net/cb/cb.aspx?a=183427

I picked one up on ebay for $50 earlier this year - haven't tried it yet.
I got it as an extra for my kids and their friends to use.

interesting - but I wonder how well getting in and out works.
looks like the zipper runs along the top of the hammock.

Marti