Late 2012 iMac becomes vintage/obsolete this month, but is eligible for pilot repair scheme - 9to5Mac
Install memory in an iMac - Apple Support
A-Tech 32GB Kit (4x8GB) RAM for Apple iMac (Late 2012, Late 2013, Late 2014, Mid 2015) | DDR3 1600MHz PC3-12800 SODIMM 204-Pin Memory Upgrade at Amazon.com
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
Apple iMac 21.5-Inch (Late 2012) Review | PCMag
Apple iMac A1418 21.5" AiO Computer i5-3330S (Late-2012) -
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
MacBook Pro 13" Unibody A1278 (Mid 2012) RAM Upgrade Kit
Memory Upgrades for iMac 21.5-Inch 2012 - Late 2013
The Case of the Late-2012 iMacs - MacStories
Install memory in an iMac - Apple Support
Apple 21.5" Pre-Owned iMac Desktop Intel Core i5 2.7GHz 8GB Memory 1TB HDD (2012) Silver MD093LL/A - Best Buy
Apple iMac 21.5” Late 2012 (A1418) Intel Core i7 3.1 Ghz 16 GB 1TB HDD | eBay