Based on personal knowledge and first-hand stories from veterans of various wars, I offer the following info.
The first Carbines in NZ were those brought here by the US Forces stationed here in WW2. They were frequently used for bush hunting (pigs & deer) on trips organised for the US troops by local hunters. These hunters were frequently rewarded with the gifts of carbines and ammo, presumably "destroyed or lost on manouvres"! A fair number were brought back from the Solomons by returning 3 NZ Div men (including my father - 1x carbine, 1x Garand, 2x Winchester Trench guns, 2x Arisakas, 2x Katanas, 1x Nambu pistol, 1x .45 auto - all stolen by wharfies in NZ!)

Some more were brought in by Korean veterans, including M2's which the NZ Police happily registered as M1's!

Some more were souvenirs of the Borneo, Malayan, and Vietnam veterans. Commercial imports were all in fairly small batches but quite a few shipments arrived, mainly in the late '60's throught to the early '80's. A lot of these were refinished and upgraded models, mainly originating in Europe (including the various German Police marked models). Some commercial models, mainly Ivor Johnson, also came in through normal trade sources.
I would suggest that most of the early and original condition carbines in NZ are those that were obtained during WW2. The US embarked on an extensive refinishing and upgrading programme after WW2 and not many original carbines survived that intact.