You have two options to resolve your dilemma. First, you can shop through a Carrier/Bryant dealer for replacement parts. Second, you can replace the entire zone control system with something new. Manufacturers of zone control systems include but are not limited to Carrier/Bryant, Honeywell, EWC, Arzel and others of somewhat lesser notoriety. It should be understood that the main purpose of a zone control system is to provide even temperatures throughout the house, not uneven. Also worthy of note is that proper system design is very important to prevent undue stress and/or more major problems with the system. A knowledgeable installing company is of the utmost importance. I would not encourage any do-it-yourself installation of a zone control system.
If YOU want change, YOU have to first change.
If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!