I need to make a spline gear that is non-circular. The pitch curves are a 360 degree spiral that acts as a pinon and a matching non-linear rack. I have the curves but am looking for a way to give them teeth.

The GearGen script only does circular gears. Is there another script or plug in that can do this? If not then is it possible to modify the GearGen script to do this?

That's going to be a tough one. Round or flat gears are just polar or linear arrays of the involute profile. Something that is non-linear/non-circular will require a different approach. Using Flow (along curve) will probably not work because it will distort the profiles. Something like ArrayAlongCurve might work - but I'm not sure if the involute needs to be different for different radii of curvature. But you might be able to find a "close enough" solution with that perhaps, there would still need to be some sort of iterative adaptation of the base curves to get an even number of teeth...

Otherwise there's probably some complex mathematics that can do this parametrically along any given curve but that's far beyond my capabilities...