Amazon.com: Timetec 8GB KIT(2x4GB) Compatible for Apple DDR3 1333MHz PC3-10600 for Mac Book Pro (Early/Late 2011 13/15/17 inch), iMac (Mid 2010, Mid/Late 2011 21.5/27 inch), Mac Mini(Mid 2011) RAM Upgrade : Electronics
A-Tech 32GB (4x8GB) RAM for Apple iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
21.5” mid-2011 iMac wires? Finally trying to upgrade my RAM and these wires are blocking the slot — did get an iMac with poor build quality? What can I do? : r/mac
HOW TO: Upgrade The RAM to 32GB on a Mid-2011 21.5inch iMac - YouTube
How to upgrade RAM on iMac 21.5" 2011 - YouTube
Install memory in an iMac - Apple Support
RAM Upgrade for iMac Mid 2011 21.5-inch | MacRumors Forums