I see, then its extremely hard to find!
I was thinking about buying the early F-mount version, but what do you think about the early S-mount? any good?
The Millennium 50mm F1.4 lens is not that hard to find on its own. Quite a few of the 10,000 or so reissue S3 Limited Edition sets that Nikon sold have been split up by now, so there's quite a few lenses only out there in the used market and they can be found with a bit of patience.
The easiest way to tell whether you're looking at a vintage sonnar optical formula Nikkor-S 5cm F1.4 lens or a gauss optical formula Millennium (Olympic) Nikkor-S 50mm F1.4 lens is to look at whether the focal length on the lens is engraved as "cm" or "mm". The sonnar lens is engraved "cm" and the gauss lens is engraved "mm".
The sonnar optical formula 50/1.4 is physically smaller, single coated, very glowy wide open but cleans up when stopped down half a stop, very sharp in the center with softer corners, and has some focus shift. The gauss optical formula Millennium 50/1.4 is larger, multi-coated, has a very flat plane of focus with excellent sharpness into the corners even wide open, and has minimal focus shift. The Millennium Nikkor is a reissue of the Olympic Nikkor released in the 1960s, so should perform similarly to the Olympic Nikkor (though I've never seen a comparison). I think the Olympic Nikkor is single coated rather than multi coated though.
There's lots of example photos taken with the sonnar Nikkor-S 50/1.4 in this
thread, along with some Millennum Nikkor shots mixed in there.
The early F-mount Nikkor-S 50mm lenses are very similar to the Olympic/Millennium lens both in optical formula and rendering, though cumbersome to use on an M-mount body as there's no focus coupling.