Apple iMac 5K Retina 27" Desktop - 4.2GHz Quad-Core i7 - 16GB RAM - 256GB SSD - AMD Radeon Pro 575 (4GB) - (2017) - Silver - Best Deal in Town
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
Apple iMac (27-inch, 2017) review: Apple doesn't mess with success - CNET
iMac Intel 21.5" Retina 4K Display (2017) RAM and SATA Hard Drive Upgrade - iFixit Repair Guide
8GB Kit (2x4GB) for Apple iMac 27-Inch "Core i5" 3.4 5K Mid-2017 Ram Memory | eBay
Install memory in an iMac - Apple Support
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