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 2017 5k iMac RAM to 64GB & Saved $840 | 2018 - YouTube
How to Upgrade/Install Memory in a 21.5-inch iMac (Mid 2017) iMac18,1 iMac18,2 - YouTube
Amazon.com: Apple 2017 iMac with 2.3GHz Intel Core i5 (21.5-inch, 16GB RAM, 1TB HDD Storage) - Silver (Renewed) : Electronics
Memory Upgrades for 2017 iMac 27-Inch
Amazon.com: Late 2017 Apple iMac Pro with 3.2GHz 8-Core Xeon (27 inch 64GB RAM, 1TB SSD) Space Gray (Renewed) : Electronics
Install memory in an iMac - Apple Support
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
Install memory in an iMac - Apple Support
A-Tech 8GB RAM for Apple iMac 2017 (27 inch Retina 5K & 21.5 inch Retina 4K) | DDR4 2400MHz SODIMM PC4-19200 1.2V 260-Pin SO-DIMM Memory Upgrade Module at Amazon.com