I wouldn't say only one in NZ just yet...
There is one in here in Gisborne running in speedway, although it is a TT142 GT-TR model (less fancy options so lighter and quicker). The guy also cut up another one (rusty as, not sure if it was a GT-T or GT-TR) which I grabbed the crossmember from to compare to my TA63 GT-TR Carina one for my Starlet project.
Could you post up the details from your chassis plate? Just curious about the cars that the 3T-GTEU came in.
I have seen other Corona turbos around occasionally but can't recall if they were GT-TR's or GT-T's. There are also two GT-TR 4 door Carina's, and a GT-TR Carina hatch around Gisborne at the moment, all looking dead standard.