Amazon.com: Original Graphics Video Card GPU Upgrade Replacement for Apple iMac 21.5 Inch Late 2011 Core i3 3.1 All-in-One Desktop PC MC978LL/A, AMD ATI Mobility Radeon HD 6750M GDDR5 512MB MXM Board :
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 :
Upgrading GPU Graphics Card on iMac 2011 - YouTube
Amazon.com: Sunvalley 2GB Graphics Video Card Replacement for Apple iMac Mid-2011 27 Inch A1312 Core i7 3.4 MD063LL/A MD063 Desktop PC Computer, ATI Radeon HD 6970 GDDR5 2 GB, New GPU Upgrade : Electronics