Have you tried talking with Dell? They may offer a replacement part.
Here's what I could find online: [http://www.ebay.com/itm/NEW-C-UV35-USB-Wireless-Bluetooth-Receiver-Dongle-DR985-820-000442-for-DELL-/131084945950?pt=PCA_Mice_Trackballs&hash=item1e85458a1e|Dell C-UV35 USB Wireless Bluetooth Receiver Dongle]. Does yours look like this?
If your keyboard & mouse are Bluetooth then any Bluetooth dongle should work. Heres one thats cheaper: [http://www.ebay.com/itm/Logitech-Unifying-Receiver-USB-Dongle-for-MK330-Wireless-Keyboard-Mouse-Combo-/121346163010?pt=Mice&hash=item1c40cb8142|Logitech Unifying Receiver USB Dongle].