I´m glad you have fun with the build
Your process is well and the idea of using styrene for spring leaf is good (I didn´t thought about)!
About the turret gear: the mounting for the gear motor, the big pinion you´ve got? That should be included in the kit.
The gear motor is available here:
Gear motor 6V 30rpm
The pinion you can get here.
pinion
because the shaft of the gear motor is 3mm, you have to reduce the bore (or maybe find one originally with bore 3mm?)
Here are two video of this model that may helps: