A-Tech 16GB (2x8GB) 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 Kit at Amazon.com
The New 2017 iMac: Notes & Tidbits on RAM - The Mac Observer
iMac 21.5-inch 4K (2017) Review | Trusted Reviews
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
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
Memory Upgrades for iMac 21.5-Inch 2017
Apple 21.5" iMac® Intel Core i5 (2.3GHz) 8GB Memory 1TB Hard Drive Silver MMQA2LL/A - Best Buy
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET