Best Buy: Logitech USB Unifying Receiver 910-005235
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
Logitech USB Unifying Receiver | Lenovo US
Logitech USB Unifying Receiver, Black | OfficeSupply.com