I do not know that they came specifically to sell arms. New Zealand military arms were always British. Brown Bess muskets, Enfield .577 Muzzleloaders, Callisher and Terry capping breech loaders, Sniders, Martini Henry then of course the ubiquitous .303 - MLM, MLE and SMLE. Official pistols included Adams and later Webley and Enfield.
A large number of 1851 Colt revolvers in .36 caliber, Adams revolvers and Tranter revolvers were used in New Zealand during the Maori Wars. The Adams and Tranters generally 54 bore (.44 cal approx) or 38 bore (.50 cal approx) The big .38 bore pistols were veritable hand cannons and developed for use in those parts of the British Empire where natives and various enemies worked themselves up into a Adrenalin fueled rush such that it took a mini cannot ball to stop them. The Adams were generally 1851 Adams or 1854 Beaumont Adams and the Tranters often 2cnd or 3rd Model and also the more conventional 4th Model
American Arms did come to New Zealand but generally privately BUT New Zealand DID buy a lot of COLT revolvers during the Maori War era, mostly 1851 Navy Colt six shot revolvers in .36 caliber but also some others were purchased by the early BNZ - Colt 1861 Navy or 1862 Police and Pocket in Navy caliber. The Otago Police also purchased, but from England quite a few Colt revolving carbines.A lot of COlt Model 1849 Pocket revolvers in .31 Caliber also came out with miners and privately - Iknow of three proven gold fields ones alone.
Other makes of arms also came out in great profusion and some very very scarce, Evans repeating rifle, Henry Brevette, Coopers revolver, transition revolvers, pepperboxes, Spencer and many others.
Well known colonial shops did import and sell a large number of American firearms including Colt revolvers and later automatic pistols up until 1921. Especially A & W McCarthy in Dunedin, Hazards of Auckland and Tisdals
Photo shows 54 bore and 38 bore 1851 Adams