Logic Board for Mid 2012 15" MacBook Pro Retina i7 2.3GHz 16GB Ram 820 - Part Haven
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
Now Here's a MacBook Pro That's Easy to Repair | WIRED
How to Upgrade MacBook Pro RAM (2009, 2010, 2011, 2012): EveryMac.com
Apple MacBook Pro (Retina, 15-inch, Mid 2012) Silver, 16GB RAM, 512GB SSD MacOS Catalina (10.15) Used (Grade C) - One Bite Technology - St. Albert