Micron 64GB (2 x 32GB) DDR4 2666MHz SODIMM Memory Upgrade Kit Compatible with 27 inch iMac (iMac19,1 iMac20,1 iMac20,2) - Walmart.com
OLOy DDR4 RAM 64GB (2x32GB) 2666 MHz CL19 1.2V 260-Pin Laptop Gaming SODIMM Upgrade for 2019/2020 iMac 27-inch with Retina 5K Display Late 2018 Mac Mini (MD4S322619MZDC) at Amazon.com
Source Dell Memory 64GB - 4RX4 DDR4 LRDIMM 2666MHz server ram 64gb ddr4 on m.alibaba.com
OWC 64GB (2 x 32GB) PC21300 DDR4 2666MHz SO-DIMMs Memory Compatible with Mac Mini 2018, iMac 2019 and up, Dell, HP, Lenovo, ASUS and Compatible PCs (OWC2666DDR4S64P) at Amazon.com
16 x 64GB PC4-21300 2666MHz | DDR4 Server Memory | Aventis