I get asked to build DIY lens gears regulary.
There are easy to make and cost pounds.
I used a company called Muffet gears.
http://www.muffettgears.co.uk/
they offer a huge range of nylon gears that can be modified to fit your housing. The teeth are the same anbd the OD's are then same oas nearly all cam gears.
The molded gears work perfectly..
http://www.muffettgears.co.uk/mould-gear.html
You will first have to count the teeth, and measure the OD of your gear...Then work ou the size of the gear.
There is info and charts on the site to see what size of gear you have.
There are many other companies at make gears near you. No need to get ripped off anymore!
Dan
B)