8GB Crucial DDR4 SO-DIMM 2400MHz CL17 Memory Module Apple iMac with Retina 5K 649528783295 | eBay
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
Crucial 16GB DDR4-2400 SODIMM Memory for Mac | CT16G4S24AM | Crucial.com
Crucial 16GB Kit (2 x 8GB) DDR4-2400 SODIMM Memory for Mac - Newegg.com
OWC 64GB DDR4 2400 MHz SO-DIMM Memory Upgrade Kit
iMac 2019 - upgraded w 2 extra ram and the speed dropped to 2400 MHz? | MacRumors Forums