Welcome MrOflam,
Yeah, I think it takes a few posts to start to get more privileges on these forums. Please don't give up on the photos, post them when you can, we'd love to see your Dromida vehicles.
Pinion gears should be very easy to find, here is a URL to one of many I quickly found (not sure what size/number of teeth your looking for).
https://www.amainhobbies.com/hot-rac...QaAs3cEALw_wcB

Maybe there is something else going on though if your having trouble setting the gear mesh?

Post some photos of your gear mesh that your having trouble with once you can, it will be easier to identify what is going on w/ a photo.