Kingston 4GB Module - DDR3L 1600MHz Server Premier - 4 GB - DDR3 SDRAM - 1600 MHz DDR3-1600/PC3-12800 - 1.35 V - ECC - Unbuffered - 240-pin - DIMM - KVR16LE11S8/4KF at Amazon.com
OWC 8GB PC3-12800 DDR3L 1600MHz SO-DIMM 204 Pin CL11 Memory Module Upgrade Compatible with iMac, Mac Mini, and MacBook Pro (OWC1600DDR3S8GB) at Amazon .com