Hynix 4GB PC3-12800 (DDR3-1600) DIMM 1600 MHz PC3-12800 DDR3 SDRAM Memory (HMT351U6CFR8C-PB) for sale online | eBay
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