How Can I Find a Doctor That Can Perform a Zygomatic Osteotomy?

I would strongly recommend going to a board certified plastic surgeon, facial plastic surgeon or oral surgeon who has experience in facial fractures to  take care of your problem. I do not believe that most "facial cosmetic surgeons" would have that experience. 

I personally would pick a craniofacial surgeon board certified by the American Board of Plastic Surgery - see below link

Based on your description of your zygomatic concern, it sounds like there is a protrusion of the arc portion of the zygoma from the buckling of the original fracture. This would also suggest that the main body of the zygoma may have rotated as well, leaving some residual cheek flatness. (decreased projection) While the traditional approach to this problem would be through the use of a coronal scalp flap (which is why your prior surgeon said the operation was too extensive for the magnitude of your problem), your zygomatic problem could be mroe easily approach from inside the mouth. A zygomatic osteotomy could be done by cutting the arch at the protrusion as well as through the main body of the zygoma. This would allow the arch segment to rotate in and the frnt part of the arch move forward. This should provide better realignment of the zygomatic arch. It would be helpful to eventually see an x-ray of this area for a more accurate assessment of the bony anatomy.