The New 2017 iMac: Notes & Tidbits on RAM - The Mac Observer
HOW TO UPGRADE NEW 2017 IMAC RAM - YouTube
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
iMac Intel 21.5" Retina 4K Display (2017) RAM and SATA Hard Drive Upgrade - iFixit Repair Guide
Install memory in an iMac - Apple Support
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
A-Tech 32GB (2x16GB) RAM for Apple iMac 2017 (27 inch Retina 5K & 21.5 inch Retina 4K) | DDR4 2400MHz SODIMM PC4-19200 2Rx8 1.2V 260-Pin SO-DIMM Memory Upgrade Kit at Amazon.com
Memory Upgrades for 2017 iMac 27-Inch
Apple 32GB (2 x 16GB) 2400MHz DDR4 SO-DIMM PC4-19200 Memory Upgrade for Late 2015-2017 iMac 27 inch with Retina 5K Display at Amazon.com