Configure your own 27-inch Apple iMac (2013) at OWC
Install memory in an iMac - Apple Support
Apple iMac 5K Retina 27" Desktop - 3.3GHz Quad-Core i5 - 24GB RAM - 1T – The Refurbished Apple Store
Install memory in an iMac - Apple Support
iMac 27-Inch "Core i7" 3.5 Late 2013 Max RAM is higher than 32gb | MacRumors Forums
27" iMac Offers Easier RAM Upgrade
SSD Upgrades for Apple iMac 27-Inch Late 2013 - 2019
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
OWC's Latest Upgrade for New Apple 2013 iMac 27” Expands Memory To 32GB, Offering Significant Savings Over Stock Apple Configurations
Install memory in an iMac - Apple Support
Pre-Owned Apple iMac 21.5-inch Desktop "Core i5" 2.9 (Late 2013) 8GB Memory 1TB HDD ME087LL/A - Best Buy
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
Install memory in an iMac - Apple Support
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