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
OWC 64GB (4 x 16GB) PC21300 DDR4 2666MHz SO-DIMMs Memory Compatible with Mac Mini 2018, iMac 2019 and up, and Compatible PCs (OWC2666DDR4S64S) at Amazon.com