Another place you can get zone control equipement is at smarthome.com http://www.smarthome.com/hvacdamper.html They claim low price guarantee but I don't know any other place you can buy some of this stuff. At least some (if not all) of their stuff is "Ultra Zone" from ewc controls, you can see it on some of the pictures on the site. I have bought stuff from smarthome and the purchases have worked out just fine. I am not affiliated with any of these companies.
Here is the manufacturer - who only sells through reps or subs: http://www.ewccontrols.com/frames.htm
This is a pretty ambitious project, hopefully you know what you are doing. If you are going to be restricting approx. 40% or more of your ducts at any time then you probably need a barometric pressure control/release. You should also probably know about having temperature sensors in your system to insure against over heating and potential freeze up in the summer - and short cycle protection, etc. I'm not saying I know all the answers, but I at least have some idea of what one would need to know to pull it off. good luck!