Check out this xbox 360 controller mount bracket for N7 2013
I was looking forever for a good mount for an xbox 360 controller since I have several laying around and no PS3 controllers, and found a 3d printed one you can buy at shapeways:
I got mine a couple days ago and it's light, a great fit and seems much more durable than it looks. You need an OTG cable to use a wired or wireless adapter for 360 controller, but works amazingly well. Especially if you pair it with Kainy and a powerful PC.