Hi MilanSalka!
I don't think they sell a separate USB receiver or dongle for their wireless keyboard/mouse as I can't find it on their store online.
You may instead contact the Microsoft Support team to inquire about it here https://support.microsoft.com/contactus/ or try it with their Microsoft Store support by going to https://www.microsoft.com/store > Click on "Questions? Talk to an expert" at the bottom of the page.