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
Install memory in an iMac - Apple Support
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
Apple iMac 5K Retina 27" Desktop - 4.2GHz Quad-Core i7 - 16GB RAM - 2. – The Refurbished Apple Store
Memory Upgrades for 2017 iMac 27-Inch
Buying a New iMac? Here's the Info on the 2017 iMac RAM Upgrades
Teardown of New 4K 21.5-inch iMac Reveals Removable RAM and Modular CPU - MacRumors
64GB Memory Upgrade Kit for 21.5-inch Apple iMac 2017
Timetec 32GB KIT(2x16GB) Compatible for Apple 2017 iMac (27-inch w/Retina 5K, 21.5-inch
Used 2017 Apple iMac 27" Core i5 3.5GHz 16GB RAM 1TB Fusion MNEA2LL/A - Walmart.com
Install memory in an iMac - Apple Support
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac