Amazon.com: Valley Of The Sun Graphics Video Card GPU Replacement for Apple iMac Mid-2010 A1311 Core i3 3.06 MC508LL/A MC508 21.5 Inch Desktop Computer, ATI Radeon HD 4670 GDDR3 256MB, MXM VGA
The IMac GPU Becomes Upgradeable, With PCIe | Hackaday
Apple opens graphics card replacement program for some mid-2011 iMacs - 9to5Mac