GT-R's are super sweet cars. And I totally get the unobtanium and therefore status they bring - plus it'd be a blast to drive. Personally, I don't know how hard or easy it would be to find parts for it. I suspect it would be a nightmare - not so much engine parts perhaps but like previously mentioned, the interior would be ridiculous.
For example, my dad has a 1987 Merkur XR4Ti. It's a Ford car (made in Germany), uses the 2.3L turbo motor. The SVO Mustang had that, so parts are reasonable. It can also use the T-5 tranny (though his is an auto) - again reasonable. Hell, even the driveline stuff like axles and rear diff and control arms (it's independent rear, not solid axle) can be found without much difficulty from a couple specialty shops, for pretty reasonable prices. That's all well and good. The problem is: this car was imported for only 3 years, and it varied slightly between years. His dash cracked. Good luck finding a replacement. All the leather on the seats is cracked. They can be re-covered, but if he has to replaced any of the seats, he's effed. If a door panel needs to be replaced? Not going to find one in the salvage yard, or probably even online. How about body panels? It's got skirts, and a funky rear decklid wing, a unique front fascia - I don't even know where he would begin to find replacements should he need it. Broken taillight? Headlight? Sorry dad. The point is: some stuff is easy(ish) to obtain, others are near impossible.
And the GT-R is even more rare than his Merkur.
So if you find one with a mint body and mint interior, you are all set. If you need to replace anything inside or on the body, the scavenger hunt begins. Not at all trying to deter you - I think owning a GT-R would be badass. It's an awesome idea, just make sure you understand the full implication of owning one - not saying you haven't thought about it - I'm sure you probably have. I just can't help but think of my dad and his Merkur - cool and very rare car to own, and near (if not actually) impossible to find half the shit he might need. If you lived in Japan, much more reasonable as the car was obtainable there (just like Merkur parts might be more obtainable in England). But you don't. But I wish you the best, I totally get wanting one of these cars (I would love one too).