Adamanta 16GB (2x8GB) Apple Memory Upgrade DDR3L 1600MHz SODIMM Compatible for iMac (Mid 2011, Late 2012, Early/Late 2013, Late 2014, Mid 2015), MacBook Pro (Early/Late 2011, Mid 2012), Mac Mini at Amazon.com
Install memory in an iMac - Apple Support
Apple Launching Pilot Program Allowing Repairs of Soon-to-Be Vintage Mid 2011 iMac in United States - MacRumors
NEMIX RAM 16GB (2x8GB Upgrade) DDR3-1333 PC3-10600 204-Pin SODIMM Memory for Apple MacBook
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com