Crucial 16GB Single DDR4 2666 MT/s (PC4-21300) DR X8 SODIMM 260-Pin Memory - CT16G4SFD8266 at Amazon.com
OWC 32GB (2 x 16GB) PC21300 DDR4 2666MHz SO-DIMMs Memory, Compatible with Mac Mini 2018, iMac 2019 and up, and Compatible PCs, (OWC2666DDR4S32P) at Amazon.com
v-Color 32GB (2 x 16GB) ECC SO-DIMM DDR4 2666MHz (PC4-21300) for NAS Micro Server/Workstation/Compatible with Synology 21 Series 2Rx8 CL19 1.2V (TES416G26D819K-VKC) at Amazon.com
Kingston 16GB ECC REG DR DDR4 2666MHZ (KTD-PE426D8/16G) at Amazon.com
Micron 16GB DDR4 SDRAM Memory Module at Amazon.com
Adamanta 16GB (1x16GB) DDR4 2666MHz (or 2133MHz or 2400MHz or 2933MHz or 3200MHz) PC4-21300 SODIMM 2Rx8 CL19 1.2v Non-ECC Unbuffered Notebook Laptop RAM Memory Upgrade at Amazon.com