G.Skill 16GB DDR3 PC3-19200 2400MHz Sniper Series (11-13-13-31) Quad Channel kit (4x4GB) 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