Sorry Andy
NSRs were definitely imported by Honda in to New Zealand in the late 80's and (maybe) very early 90's.
We definately had MC 16's and MC18's but i am not sure if we had official 21's (as i type this i think probably not).
My first race bike was an NS250 and i then went to a MC18 and then on to RGV's which were better because you could buy them new (ie unthrashed).
I still believe performance wise they were very similar but hard to confirm as all the guns at the time went RGV, although i do have a video of one international superbike support race at Manfield where the MC18 beat 20+ RGV's.
Still hard to quantify as he was probably a better rider (Dave Cole) than most of the others at the time.
Cheers
Mark