Crucial 4GB Single DDR3-1600 (PC3-12800) SODIMM 204-Pin High Density Memory CT51264BF160BJ at Amazon.com
4GB PC3-12800 DDR3L-1600 SODIMM - Walmart.com
RAM SQP SoDimm 4 GB DDR3 1600 MHz - PC3-12800 Spare Parts - SOSav English
Timetec 4GB DDR3L-1600 SODIMM - Timetecinc.com - Memory of Lifetime and Easy Upgrades
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