Apple iMac 27” Mid 2011 A1312 MC813LL/A MC814LL/A Logic Board 820-2828 - NO CPU | eBay
Amazon.com: Valley Of The Sun 2GB Graphics Video Card Upgrade for Apple iMac Mid-2011 27 Inch Core i5 MC814LL/A MC814 A1312 Desktop All-in-One PC, AMD Mobility Radeon HD 6970M Replacement Repair Parts :
iRepair - iMac Samsung Pro SSD and Intel i7 CPU upgrade | Facebook
21.5 iMac Mid 2011 12,1 A1311 820-3126 Logic Board Core I5 "CPU Not In - Part Haven
2011 imac 27" 32GB - final stage of 1TB + 2TB SSD upgrade (replaced HDD & optic drive). Also cleaned out the fans and case. Running 'SSD Fan Control' & 'Macs Fan
Amazon.com: Odyson - Logic Board Replacement for iMac 21.5" A1311 (Mid 2011, Late 2011) : Electronics
Apple iMac 21.5" All-in-One Desktop Computer i3 3.07GHz 4GB Ram 500GB HDD Mac OS High Sierra MC508LL/A w/ Keyboard & Mouse
Upgrade iMac Intel Core i3 CPU to Core i7 - iFixit Repair Guide
Best Buy: Apple® iMac® / Intel® Core™ i3 Processor / 27" Display / 4GB Memory / 1TB Hard Drive MC510LL/A