ThinkPad T420 Hard Drive Replacement - iFixit Repair Guide
Amazon.com: CMS 128GB mSATA 6GB/s Internal SSD Compatible with Lenovo ThinkPad T420 Series - C29 : Electronics
Amazon.com: Bfenown 2nd HDD SSD Hard Drive Caddy Tray Replacement for Lenovo Thinkpad T420 T430 T510 T520 T530 W510 W520 W530, Internal Laptop CD DVD ROM Optical Modular Bay to 2.5 Inch
Lenovo ThinkPad T440 m.2 SSD and 2.5" SSD Install (how to + test run) - YouTube
Nimitz 2nd HDD SSD Hard Drive Caddy Compatible With Lenovo ThinkPad T420 T430... for sale online | eBay