A-Tech 16GB (4x4GB) RAM for Apple iMac 2017 27 inch Retina 5K | DDR4 2400MHz SODIMM PC4-19200 1.2V 260-Pin SO-DIMM Memory Upgrade Kit at Amazon.com
16GB DDR4 2400MHz PC4-19200 SO-DIMM RAM Memory Upgrade for 2017 iMac 27 inch with 5K Retina Display (PARTS-QUICK) - Walmart.com
Crucial 16GB DDR4-2400 SODIMM Memory for Mac | CT16G4S24AM | Crucial.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