When you look at fans you want to pay attention to the cubic feet per minute value. This is how much air it actually pushes or pulls.
That fan is about 95 CFM, which is very good. It's a 120mm case fan. For most computer systems 75 CFM is considered "great". 95 CFM is extremely high (Though there are higher).
These are super common, just take a look through the endless lists of 12v 120mm case fans.
For instance:
http://www.newegg.com/Product/Product.a ... 6835213001
It's a 6v-12.8v fan (which is how speed is controlled), maximum speed is 5200 RPM, creating 240 CFM. Which is insane. It's also very loud at 62 dBA. That's about the loudness of a washing machine.
There's all sorts of fans, they're all in the same price range. You could do the mod differently if you haven't done it yet using smaller fans and more strategic airflow. Or you could get a larger fan that moves slower (which is actually what the PS3 does)
But the main issue with the 360's air flow is there's no real intake. If you're sitting it horizontal, the only available intake is the right hand side (opposite of the HDD). You could attempt to mount dual 80mm fans there. That would probably help greatly.
I would also imagine mounting fans to the actual heatsinks would work better, so it can pull heat away.
How is this oriented, anyway? It looks like it's pushing air in.
