SOLVED: Are these the right SSD PCIe blades for iMac Late 2013? - iMac Intel 21.5" EMC 2638 - iFixit
Timetec 256GB MAC SSD NVMe PCIe Gen3x4 3D NAND TLC Internal SSD Compatible with Apple MacBook Air (2013-2015, 2017), MacBook Pro (2013-2015), iMac ( 2013-2019), Mac Pro (2013), Mac Mini (2014) - Walmart.com
Apple iMac (27-inch, September 2013) review: New processors and faster Wi-Fi for Apple's slim desktop - CNET
An External SSD Gave My iMac a New Lease on Life - TidBITS
Amazon.com: Sintech M.2 nVME SSD Adapter Card Upgrade Kits,Compatible for MacBook Air(2013-2017 Year) and MacBook PRO(Late 2013-2015 Year,iMac : Electronics
Timetec 256GB MAC SSD NVMe PCIe Gen3x4 3D NAND TLC Internal SSD Compatible with Apple MacBook Air (2013-2015, 2017), MacBook Pro (2013-2015), iMac ( 2013-2019), Mac Pro (2013), Mac Mini (2014) - Walmart.com
NEW 2TB SSD For Apple MacBook Pro 13" / 15" iMac 21.5" 27" Late 2012 Early 2013 | eBay