Dual throttles for 912iS?

There are various aircraft, like the Zenith you mentioned, that incorporate a dual throttle setup. However, we're not aware of any dual-throttle kits available. Instead, this tends to be a unique design feature tailored for specific aircraft models. If you could provide more details about your aircraft type, there's a chance the manufacturer might have already developed a solution. If not, you might need to take the initiative to design and engineer a custom solution yourself.