Configure your own 27-inch Apple iMac (2013) at OWC
Apple iMac (27-Inch, Late 2013) - Core i7-4771 3.5 GHz, 32GB RAM, 3TB Fusion, 775M - WBAM
iMac (27-inch, Late 2013) - Technical Specifications
Apple iMac 27" All-in-one A1419 Late 2013 i5 3.4GHz 32GB Ram 3TB 1 Year Warranty | eBay
Timetec 32GB KIT(4x8GB) Compatible for Apple DDR3L 1600MHz PC3L-12800 CL11 for iMac (Mid 2011, Late 2012, Late 2013, Late 2014 Retina 5K, Mid 2015 Retina 5K) SODIMM Memory Module MAC RAM Upgrade at Amazon.com
Apple iMac 27-inch 3.2GHz Quad Core i5 32GB RAM 1TB HD NVIDIA 755M 1GB ,2013 | eBay
27in iMac Late 2013 - 32GB RAM - 500GB SSD - i5 for Sale in Glendale, CA - OfferUp
timetec 32gb kit(4x8gb) compatible for apple ddr3l 1600mhz pc3l-12800 cl11 for imac (mid 2011, late 2012, late 2013, late 2014 retina 5k, mid 2015 retina 5k) sodimm memory module mac ram upgrade - Walmart.com
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET