How to Upgrade Memory in a 21.5-inch or 27-inch iMac (Mid 2010) - YouTube
CMS 16GB (4X4GB) DDR3 10600 1333MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core I3 3.06 21.5-Inch (Mid-2010) - A28 at Amazon.com
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
32.0GB OWC Memory Upgrade Kit For 2010-2011 Apple iMac
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
Timetec Hynix IC 32GB KIT(4x8GB) Compatible for Apple 27 inch Mid 2010 21.5/27 inch Mid 2011 iMac DDR3 1333MHz PC3-10600 CL9 204 Pin SODIMM Upgrade for iMac 11,3 iMac 12,1 iMac 12, 2 (32GB KIT(4x8GB)) - Newegg.com
NEMIX RAM 32GB (4x8GB Upgrade) DDR3-1333 PC3-10600 204-Pin SODIMM Memory for Apple MacBook Pro Early/Late 2011, iMac Mid 2010 27 inch 4-Core, iMac Mid 2011 21.5/27” , Mac Mini Mid 2011 at Amazon.com
Timetec Hynix IC 8GB Compatible for Apple DDR3 PC3-8500 1067MHz /1066MHz SODIMM Memory Upgrade for MacBook 13'' Mid 2010, MacBook Pro 13'' Mid 2010, iMac 27''Late 2009, Mac Mini Mid 2010 (8GB) - Newegg.com
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
Apple iMac 27-inch, Mid 2010 Memory 4 GB. Not Used Since 2015 | eBay
Upgrading my Mid 2010 Imac computer | MacRumors Forums