Amazon.com: Logitech USB 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
SummitLink Unifying Receiver for Mouse and Keyboard Compatible for Any Logitech Product That Display The Unifying Logo (Orange Star, Connects up to 6 Devices) B083J7DYDT
Genuine Logitech Unifying Mirco Dongle Receiver USB For keyboard K400r K400plus | eBay
Logitech K400 Plus Wireless Touch Keyboard 920-007119 B&H Photo
Logitech K400 Black Wireless Keyboard with Built-In Touchpad & USB Receiver | eBay