amd64.org website appears to be down, where is CPU microcode available from? and where will the updates to it published?
Is your request for a specific AMD CPU family and if so, which one? Also can you share the reason you are asking?
Generally, AMD provides microcode as part of the system BIOS or UEFI firmware. If an update is necessary, it may be provided to various Linux distribution providers such as an installable package, and will be published on the kernel.org linux-firmware git repository.