Amazon.com: OWC SSD Upgrade Kit for 2010 27-inch iMacs, Mercury Electra 500GB 6G SSD, 18" SATA III 6Gbps Data Cable, SSD Power Cable, Installation Tools and iMac Screen Adhesive Tape Set :
2nd SSD HDD Hard Drive Tray Caddy for 27" 21.5 iMac mid late 2009 2010 2011 2012 | eBay
OWC Internal SSD DIY Add-On Kit with Tools (for 27" Apple iMac Mid-2010) | eBay
iMac (mid-2010) SSD Upgrade with Samsung 850 Evo - YouTube
Apple iMac A1311 21.5 inch 12GB RAM 500GB SSD Desktop - MC508LL/A (July, 2010) 885909389131 | eBay
Amazon.com: 2nd HDD SSD Hard Drive Caddy for Apple iMac Mid-2010 A1311 MC508LL/A MC509LL/A MC508 MC509 21.5-Inch Desktop Computer, SATA 3 Second Solid State Drive Enclosure, CD DVD SuperDrive Optical Bay :
Apple iMac 2010 (Mid) 21.5-inch (iMac 11,2) SSD ,Ram & OSX Upgrades - ZD Laptop Service Centre
Installing additional SSD in Mid-2010 27" iMac
iMac 27" 21.5" 480GB-1TB SSD Upgrade Service 2010 - 2019 Inc Data Migration | eBay
OWC SSD Upgrade Kits For 21.5-Inch iMac 2010
What you can do with an internal SSD module from a vintage Mac | Macworld