A-Tech 4GB RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010, Mid 2011, Late 2011), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Module at Amazon.com
4GB PC10600 DDR3 1333MHz SO-DIMM Memory Compatible with 2011 MacBook Pro, Mid 2010/2011 21.5" & 27" iMac Models, 2011 Mac Mini (OWC1333DDR3S4GB) at Amazon.com
A-Tech 4GB RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010, Mid 2011, Late 2011), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Module at Amazon.com
Apple MC309LL/A 21.5" iMac Computer Core i5 2.7 GHz 4GB RAM 1TB HD Mid-2011 | RecycledGoods.com
16GB Kit (4 x 4GB) PC3-10600 RAM for Apple iMac Mid 2011 - 27 Inch MC814LL/A Memory Upgrade Kit
Used Apple iMac 21.5" Mid 2011 i5-2400S 4GB DDR3 RAM 500GB HDD El Capitan Tested | eBay
A-Tech for Apple 8GB Kit 2 x 4GB PC3-10600 Mac Mini iMac MacBook Pro Mid 2010 Late 2011 A1286 MD311LL/A A1297 MC511LL/A A1312 MC309LL/A A1311 MC812LL/A MC813LL/A MC814LL/A MC815LL/A A1347 Memory RAM