A-Tech 16GB Kit (2x8GB) RAM for Apple MacBook Pro (Mid 2012), iMac (Late 2012, Early/Late 2013, Late 2014, Mid 2015), Mac Mini (Late 2012) | DDR3 1600MHz PC3-12800 SODIMM 204-Pin Memory Upgrade at Amazon.com
MacBook Pro (13-inch, Mid 2012) Hard Drive (and possibly RAM) replacement : r/mac
Memory RAM Upgrades for MacBook Pro (2012 - Late 2016)
A-Tech 8GB RAM for Apple MacBook Pro (Mid 2012), iMac (Late 2012, Early/Late 2013, Late 2014, Mid 2015), Mac Mini (Late 2012) | DDR3 1600MHz PC3-12800 SODIMM 204-Pin Memory Upgrade at Amazon.com
How to upgrade the RAM on your 13-inch MacBook Pro
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
MacBook Pro: How to remove or install memory - Apple Support
CMS 16GB (2X8GB) DDR3 12800 1600MHz Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® MacBook Pro Core I5 2.5 13" Mid-2012 - A7 at Amazon.com
MacBook Pro 13" Unibody A1278 (Mid 2012) RAM Upgrade Kit