OWC 4GB PC12800 DDR3L 1600MHz SO-DIMM Memory Compatible with 2011-2015 iMac, 2011-12 Mac Mini, and 2011-2012 MacBook Pro (Non-Retina Display) Models (OWC1600DDR3S4GB) at Amazon.com
P000574810 Toshiba 4GB SODIMM Laptop Memory
Kingston 4GB 1600MHz PC3-12800 1.35V SODIMM DDR3L Memory at Amazon.com