The Japs keep the 'cream of the crop' so to speak, for themselves. I'm sure the big specialist 'Line yards over there are happy to let us gaijins take their slightly more used-and-abused examples off their hands LOL.
42,000+ may seem like a lot, but the Jap population is huge, so you would have to assume there are a good number of young guys looking to get into a GT-R as soon as they get their licence theses days, if they can afford it (much like here- 'cept our rego is much cheaper in comparison).