Yeah there are fans bigger than 120mm, but I don't think you can mount one unless you modify your case.
Just for fun, here is the spec for a circular 172x150x50mm DC fan:
Voltage - 24v
Current - 0.87a
Power - 20.88W
Speed - 3000rpm
AirFlow -
217.7CFM
Noise - 53.9dBA
Weight 613g
If someone actually put a couple of these fans in their system I wouldn't be surprised to see it starts levitating off the ground like a hovercraft...
Tony