: Locked to the first motherboard it is activated on and cannot be moved.
Since official sales have ceased, your primary source will be third-party sellers who stock "New Old Stock" (unused physical boxes) or OEM licenses: where to buy windows 8.1 pro
: Bulk license platforms like Alibaba frequently list Windows 8.1 Pro keys, though these are often intended for volume licensing or OEM use. : Locked to the first motherboard it is