I thought it would be good to start a thread with vendors for Z6 accessories, as I'm sure there are plenty of people out there looking for stuff. Here's my list of places to look:
http://www.superatv.com/ Our forum's supporting vendor, so it's good to support them, but I don't think they have anything Z6 specific. Plenty of their universal stuff could probably be adapted though, and that universal power steering kit is intriguing. I'm sure their light bars could we wired in as easily as on any other machine.
http://www.sidebysidestuff.com/ These guys do actually have a number of Z6 specific accessories, most notably a full
FOLDING windshield, which I am drooling over.
http://www.scapdoors.com/ Doors for the 600!
http://www.ironbaltic.com/ironbaltic_home/ Iron Baltic offers a good skid plate, as well as mounting kits for snow plows, and the plows themselves. They also have a winch mounting kit, not sure why you'd need it though, as the Z6 comes with a winch.
http://www.electronicjetkit.com/ EJK makes an EFI controller specific to the Z6 if you want to adjust your fuel/air mixture.
I believe that the Camoplast/Camso T4S track system can be mounted on a Z6, but I think you'll need to talk to a Camoplast dealer; their website isn't real great for just selecting a part for a particular vehicle and trying to order it.
Airdam will do whatever it is that they do to your clutch, if you pull it off and ship it to them, or you could probably order a full clutch from them. My guess is that they just tune it for whatever modifications you've done, but I don't really know that much about it.
CF MOTO Canada's website lists doors, brush bumpers, a tilting windshield, and a fender flare kit, I think you could probably talk to your US dealer about special ordering them, but I'm not sure on the specifics of getting them if you're not in Canada. I'm sure it could be done though.
That's everything I know about, feel free to chime in if you know of anything else!