Amazon.com: GDDR5 2GB Graphics Video Card Radeon HD 6970M for Apple iMac Mid-2011 27 Inch Core i5 i7 All-in-One Desktop PC Computer, AMD Radeon HD6970M HD6970 MXM Board GPU Upgrade Repair Parts :
FOR DELL Alienware M17xR3 M18x AMD Radeon 6970M 2GB Video Graphics Card 06W46K | eBay
iMac 27' (mid 2011) fix for AMD Radeon HD 6970M no video problem - YouTube