What about these, though they are made for the corolla?
http://www.ebay.com/itm/BULLET-MIRROR-FENDER-HAND-MADE-FOR-RETRO-CAR-TOYOTA-CELICA-COROLLA-CORONA-BLACK-/222334979066?hash=item33c4328bfa:g:CKkAAOSwo4pYUBRo&vxp=mtr
The back seat on a 300zx is useless! Its good for a couple bags of groceries and not much else. Keep in mind that this car sets low to the ground so your grandfather might have a hard time getting up out of the car.
http://www.japaneseclassicsllc.com/1989-nissan-fairlady-z-300zx-twin-turbo-7995.html