I have just attached the only fan i could find that was close to the right size.
Screws wouldnt line up right with the holes in the fan so i used very small zip ties.
Works great, i can actually touch the heat sink without getting burned.
I still want one of the stock Gigabyte fans though.
This thing is louder than any other fan i've ever used, and doesnt look nearly as nice as one of the stock ones would.