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, MXM VGA Board Repair
How to Upgrade/Replace GPU Graphics Card on Mid-2011 21.5" iMac - YouTube
For iMac 27" A1312 Mid 2009 2011 HD6970M upgrade NVIDIA GTX 765M 2GB Video Card | eBay
Apple Initiates Video Card Replacement Program for Radeon HD 6970M Equipped Mid-2011 27” iMacs
For iMac 27" A1312 Mid 2009 2010 2011 upgrade NVIDIA GTX 880M 8GB Video Card | eBay
Upgrading an iMac GPU for METAL Support! Late 2009 – Mid 2011 Models - YouTube