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
Logitech K520 Wireless keyboard with mouse and Receiver Unifying. Like a New | eBay
Logitech K520 Wireless Keyboard (NO RECEIVER) 97855103246 | eBay
Logitech Unifying Receiver for Connecting Multiple Devices