Id like to scale this down but need an alternative to the curvic as I don't see them offered in a smaller size.
Maybe pins and bushings ? Or keys and slots ?
You need them tapered for it to work at all. Otherwise a small lash and vibrations are inevitable. If you have an accurate enough CNC mill I think it wouldn't be a problem making one. If your mill isn't accurate you should still get around if you have a rotary table which would index one tooth at a time and the mill would cut each tooth at the same location, thus repeatability is guaranteed.