iMac Intel 27" Mid 2011 EMC 2429 - used original spareparts for Macs
A-Tech 8GB RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Module at Amazon.com
A-Tech 16GB (4x4GB) RAM for Apple iMac (Mid 2010, Mid 2011, Late 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
I recently purchased 2011 21.5 iMac (Mid-2011) and I'm obsessed. : r/mac
Install memory in an iMac - Apple Support
APPLE IMAC A1311 Mid 2011 21.5" i5-2400S 8GB RAM 500GB HDD FHD Yosemite Radeon $126.65 - PicClick AU