[MrForbes]

Are you talking about the gears that are inside the FP gearbox, that are molded plastic, and have two gears molded together, one with small teeth and one with large teeth?

If so, I don't know of any place where you can buy random sized gears like that, you need to either use some from a gearbox like the FP gearbox, or else connect two different gears together, on a common shaft.