Apple Memory Module 16GB DDR4 2400MHz SO-DIMM (2x8GB) - Apple
CMS 8GB (2X4GB) DDR4 19200 2400MHZ NON ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core i5 3.5 27-Inch 5K Mid-2017 MNEA2LL/A - D6 System Specific Memory - Newegg.com
DDR4 2400MHz PC4-19200 for Apple iMac 21.5" 18,1 & 18,2
iMac 2017 RAM update, running smoothly on 3200MHz DDR4, higher than 2400MHz Recommendation : r/mac
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 Memory Module 32GB DDR4 2400MHz SO-DIMM (2x16GB) | Bridge Street Town Centre
Amazon.com: OWC 64GB (4 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with 27" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S64S) : Everything Else
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