Welcome aboard.
The genuine Nismo 350Z was only available in Japan & America with AFAIK only ever one being imported into the UK, ...which was apparently done by a Nissan dealership.
Some more info on the 350's can be found here: https://en.wikipedia.org/wiki/Nissan_350Z
You can of course pay extra if you like for a "so called" Nismo 350Z because of all the extra parts fitted (stickers, badges, skirts etc) but just be aware that it won't be a genuine Nismo.
If you are so inclined you could always just pay less for a decent 350Z GT and then add the extra mods you want afterwards which is what I'd do.