Amazon.com: Logitech Unifying Receiver, 2.4 GHz Wireless Technology, USB Plug Compatible with all Logitech Unifying Devices like Wireless Mouse and Keyboard, PC / Mac / Laptop - Black : Electronics
Genuine Logitech Unifying Mirco Dongle Receiver USB For keyboard K400r K400plus | eBay
Logi Bolt USB Receiver for Multi-Computer / Device Use
Replacing Your Wireless Mouse / Keyboard Receiver - ComeauSoftware.com
SOLVED: USB for wireless Logitech keyboard lost. - Logitech Harmony Smart Keyboard - iFixit