128GB FUSION DRIVE PCIe SSD Apple iMac 21.5" A1418,27" A1419 Late 2013,2014,2015 | eBay
Original 128GB PCI-e SSD Replacement for MacBook Pro Late 2013 - Mid 2014, MacBook Air Mid 2013 - Early 2014, iMac Late 2013 - Mid 2015, Mac Mini Late 2014 (Bulk, No Retail Packaging) : Electronics
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21.5" inch Late 2013 iMac A1418 Hard Drive SSD Upgrade Replacement Repair - YouTube
iMac 2013 sees iFixit teardown: SSD slot free for upgrade - SlashGear