Hi JJ_SV,
to purchase Windows Server 2022 Standard, you can visit the Microsoft Store or contact a Microsoft authorized reseller.
The licensing for Windows Server 2022 Standard is based on the number of physical cores in the server. In your case, since each node has 1 CPU with 12 cores, you will need to purchase a total of 36 core licenses (3 nodes x 1 CPU x 12 cores per CPU). You can purchase these licenses either as a pack of 16 core licenses or as individual core licenses.
Once you have purchased the necessary licenses, you can install Windows Server 2022 Standard on each node and activate it using the license key provided.
Hope this helps.
Kind regards,
Lei