You can find them at http://www.shelter-systems.com/ and their site is *well* worth a dig-through for anyone interested in this sort of thing. (Chances are, that's you, or you wouldn't be reading this page. :-) )
Interestingly enough, I found out a few months ago that a friend of mine is good friends with the guy behind Shelter Systems. It's interesting how the circles cross, isn't it? :-)
I'm considering his [Grip Clips] for use with the film/fabric covers for the greenhouse kits I'd like to make. And actually, given the amount of work he's put into developing the various systems already, it might make good sense to partner with him in some way. Perhaps selling dome kits paired with greenhouse covers pre-made by Shelter Systems.
For more info and background on the greenhouse/dome kit idea, check the [Contributions and Support - Projects Page].
PS - Completely off-topic, but cool nonetheless, this is the 100th page in this wiki! :-)