Hello,
Thanks for reaching out! I'm Microsoft user like you.
The USB dongle and Microsoft keyboard are a set and arrive as a matched pair. The dongles are not interchangeable.
The device and receiver have the same frequency. Since the USB dongle is programmed specifically for your device, a replacement cannot be obtained.
However you can try to connect with Microsoft support using below link.
https://support.microsoft.com/contactus -> Select PC accessories
In case of additional questions, reach out back to me, and I will be happy to help and try our best to resolve your issue.
Best Regards,
Prakash