there are plenty of threads about non-GMH rotors - plenty of people buy them and are happy with their purchase.
Some dealers put larger brakes on V6, before the car leaves the showroom.
They have stacks of brand-new, smaller rotors, going cheap.
Last year I picked up two fronts plus two rears, all new, for $20 each, total $80, from a dealer in North Melbourne, via Ebay.
If I had been willing to go to Sheparton V, the Holden dealer was selling complete sets of rotors AND pads for $80 - again on Ebay.