Nemix Ram 128GB Memory for Apple iMac Pro 1, 1 (27-inch Late 2017-Current) 2X64GB DDR4 2666Mhz PC4-21300 288-Pin LRDIMM Ram Memory Module at Amazon.com
RAM UPGRADE - iMac Pro A1862, 2017, installation included.
iMac Pro Release Date, UK Price & Specs
iMac Pro teardown reveals what you can upgrade and what you can't | Ars Technica