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
Amazon.com: Logitech New Unifying USB Receiver for Mouse Keyboard M515 M570 M600 N305 MK330 MK520 MK710 MK605 : Electronics
3 LOT Logitech K520 Wireless Keyboard M325 Mouse + Unifying Receiver USB Dongle | eBay
Logitech K520 Wireless Keyboard With Unifying Receiver Dongle! | eBay