Hi Chris,
I'm Dyari. Thanks for reaching out. I will be happy to assist you in this regard.
I am afraid that you can not get an OEM license separately as this type of license is tied to the motherboard when you buy it from the supplier. Also, cheap licenses found online are usually not genuine as most of them are temporary and work only for a short period of time. So, please be careful of buying licenses from an unauthorized reseller.
https://www.microsoft.com/en-us/howtotell/Shop....
The best place to purchase genuine Windows license keys is from the Microsoft official website:
https://support.microsoft.com/en-us/windows/act....
Regarding upgrading Windows 10 to Windows 11, kindly run the PC Health Check app to see if your computer supports Windows 11 or not:
https://support.microsoft.com/en-us/windows/how...
Please let me know if you need further assistance and keep me updated.