Kingston 4GB 1600MHz SODIMM DDR3 1600 Memory Module for HP (PC3 12800) KTH-X3C/4G at Amazon.com
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
Amazon.com: Crucial 4GB Single DDR3/DDR3L 1600 MT/s (PC3-12800) SODIMM 204-Pin Memory For Mac - CT4G3S160BM : Everything Else