Check out our (virtually only) model shop in Auckland (100km round trip) which has truckloads of plane, plastic kitsets, scale cars, a 30ft wall of just fittings, everything you might need except boat stuff. Most of the boat kits are out of stock as they can't get them (and probably not the interest any more to warrant the cost, also expensive to ship down here) Most model shops had boat gear years ago, but you might as well say non existent now.
Another shop, Acorn models in Christchurch (2,205km round trip -cross strait ferry included- or a 2hr 40min return flight) had a branch in Auckland but has shrunk back to it's original home, and now doesn't appear to hold much boat gear either,- was a very big outfit years ago.
One of the original model shops -Modelair in Auckland (where I bought my first boat radio - OS Cougar 2ch- first marine motor,- OS 30, and plan for my old Vic Smeed MTB back in the late 60s amongst lots of other models) has changed hands a few times over the years and has pretty much disappeared.
There are a few small outfits which operate from home or on line only, but we are not exactly spoilt for choice. Quite often the Kiwi No 8 wire technology has to be utilised. Uncle Alis' is our new shop now for boat stuff,- either that or build planes.
Have a look inside Hobby city (360 view) on the google directory screen on right of page (search Hobby City separately on google and you should see it) Same thing with Acorn Models
https://hobbystation.co.nz/ Is another in Auckland owned by a Chinese guy, (has access to cheap stuff direct but rorts the price here ) which is supposedly ok (yet to visit) Most small model shops just sell cars or plastic kits, so don't really count.