Amazon.com: Timetec 4GB Compatible for Apple DDR3 1333MHz PC3-10600 CL9 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) SODIMM MAC RAM Upgrade : Electronics
4GB DDR3 1333MHz RAM ~ for Apple iMac Mid 2010 & Mid 2011 Memory | eBay
Top Tier PC3-10600 SO-DIMM - 4GB DDR3 1333MHz | Sweetwater
OWC 16.0GB (4 x 4.0GB) 1333MHz DDR3 ECC PC8500 SDRAM PC3-10600 Memory Upgrade Kit (OWC1333D3W4M16K) at Amazon.com
4GB Memory for 2011 MacBook Pro, iMac, and Mac mini
8GB 2X 4GB Memory Compatible for Apple iMac Core i3 i5 i7 Mid 2010 DDR3 PC3-10600 204 pin 1333MHz SODIMM RAM (PARTS-QUICK Brand) at Amazon.com
Apple iMac 27" Desktop - MacOS High Sierra 10.13.6 (mid 2010) 4GB 1333 MHz DDR3 | eBay