Timetec 4GB DDR3L-1600 UDIMM - Timetecinc.com - Memory of Lifetime and Easy Upgrades
Kingston 4GB 1600MHz PC3-12800 1.35V SODIMM DDR3L Memory at Amazon.com
OWC 12GB (8GB+4GB) PC3-12800 DDR3L 1600MHz SO-DIMM 204 Pin CL11 Memory Upgrade Kit Compatible with iMac, Mac Mini, and MacBook Pro (OWC1600DDR3S12S) at Amazon.com