check those online stores like greenline, takakaira, nengun. they usually deal with originals, some brands offer that flexi compound some dont so you have to doubel check. From what you described i think your still gonna have scraping issues with the roads and driveways you use cause alot of the aftermarket bars are a heck of a lot lower than a stock gtr one. Your on the money though with the gtr one as it has a botom lip that can be taken off for repairs.
If you can source all parts for a decent price it maybe worth a shot, might have to flare the rear guards out abit...then you may need new rims to sit flush with the wheel archs? will your sideskirts fit the gtr pannels? alot to think about, would be a good project non the less. those gtr headlights with projectors look hot.