Amazon.com: OWC 8GB (2 x 4GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S08P) : Everything Else
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
Crucial 8GB DDR4-2400 SODIMM Memory for Mac | CT8G4S24AM | Crucial.com
Apple Memory Module 32GB DDR4 2400MHz SO-DIMM (2x16GB) - Apple
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 16GB DDR4 2400MHz SO-DIMM (2x8GB) - Apple