64GB (4 X 16GB) Kit Memory Module for Apple iMac 27" 2017 5K Retina Display DDR4 2400MHz SO-DIMM RAM (PARTS-QUICK Brand) at Amazon.com
Adamanta 128GB (4x32GB) Memory Upgrade for 2020 Apple iMac 27" w/Retina 5K Display & 2019 Apple iMac 27" w/Retina 5K Display DDR4 2666Mhz PC4-21300 SODIMM 2Rx8 CL19 1.2v DRAM RAM : Electronics
Timetec 32GB KIT(2x16GB) Compatible for Apple DDR4 2666MHz / 2667MHz for Mid 2020 iMac (20,1/20,2) / Mid 2019 iMac (19,1) 27-inch w/Retina 5K, Late 2018 Mac Mini (8,1) PC4-21333 /PC4-21300 MAC RAM : Electronics
iMac Retina 5K: Memory upgrade (RAM)
How to upgrade the 27-inch 5K iMac (2019) with a massive 128GB of RAM [Video] - 9to5Mac
Memory Upgrades for iMac w/ Retina 5K Display Late 2015
A-Tech 16GB (2x8GB) RAM for Apple iMac 2017 (27 inch Retina 5K & 21.5 inch Retina 4K) | DDR4 2400MHz SODIMM PC4-19200 1.2V 260-Pin SO-DIMM Memory Upgrade Kit at Amazon.com
Adamanta 16GB (2x8GB) Memory Upgrade for 2020 Apple iMac 27" w/Retina 5K Display, 2019 Apple iMac 27" w/Retina 5K Display, 2018 Apple Mac Mini DDR4 2666Mhz PC4-21300 SODIMM 1Rx8 CL19 1.2v DRAM