parts-quick 8GB (2 X 4GB) Kit Memory Module for Apple iMac 27" 2017 5K Retina Display DDR4 2400MHz SO-DIMM RAM at Amazon.com
Amazon.com: v-Color 16GB(2x8GB) DDR4 2400MHz for iMac 2017 27-inch w/Retina 5K Display & 21.5-inch w/Retina 4K or Non-Retina Display iMac Non ECC SO-DIMM CL17 1.2V (TN48G24S817K-VC) : Everything Else
OWC2400DDR4S16P Other World Computing DDR4, KIT, 16 GB: 2 X 8 GB, SO-DIMM 260-PIN, 2400 MHZ / PC4-19200, CL17, 1.2 V, UNBUFFERED, NON-ECC, UPGRADE, FOR APPLE IMAC (MID 2017) : PartsSource : PartsSource - Healthcare Products and Solutions
parts-quick 8GB (2 X 4GB) Kit Memory Module for Apple iMac 27" 2017 5K Retina Display DDR4 2400MHz SO-DIMM RAM at Amazon.com
Apple 32GB (2 x 16GB) 2400MHz DDR4 SO-DIMM PC4-19200 Memory Upgrade for Late 2015-2017 iMac 27 inch with Retina 5K Display at Amazon.com
Amazon.com: OWC 32GB (2 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S32P) : Everything Else