Amazon.com: INDMEM 512GB NVMe PCIe SSD 3D TLC NAND Flash Hard Drive Disk 512G Only for Late 2013 - Mid 2015 MacBook Pro, Mid 2013-2017 MacBook Air, Late 2013-2017 iMac, Late 2013
SSD Replacement Kit - iMac A1418 (2013-2014)
2013 iMac teardowns reveal SSD slots, soldered-in CPU in the 21.5” model | Ars Technica
How to Upgrade/Replace the PCIe SSD in a 21.5-inch iMac (Late 2013) on Vimeo