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
Logitech Unifying USB Receiver for Wireless Mouse and Keyboard, 6-Device (910-005235) | Staples
Logitech K400 Plus did not come with a USB dongle? Wait!! It's hidden in the box!! | THINKBOX
Genuine Logitech Unifying Mirco Dongle Receiver USB For keyboard K400r K400plus | eBay
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 USB Unifying Receiver - 2 Pack For Personal Computer : Electronics