Great your sorted with the CAM side then and often that's the hard part so your off to a good start.

Sorry can't help with where to go for dedicated parts for this mill but for Motors and drives etc then Gary at Zapp is good start.
Ballscrews will depend on diameter size and pitch your wanting. To be honest I think your biggest problem will be getting ballscrews to fit and Big chance your going to need to modifie the base or bed in some way to make room. Unfortunatly I've no experience with these small mills so can't help here.!