CPUs do not have non-volatile memory for storing microcode updates. It has to be uploaded from the motherboard during the boot process, and the OS can optionall

CPUs do not have non-volatile memory for storing microcode updates. It has to be uploaded from the motherboard during the boot process, and the OS can optionally upload a newer version as part of their boot process. So the difficult thing is finding a matching motherboard that's running an old enough firmware version, or that can be rolled back to an older firmware version.