I will make it easy for you.
Importers order their stock from overseas. They don't see it first. NZ is a small market so the best pieces go to the suppliers best customers and biggest customers - so not NZ.
Shops order stock from importers. They don't see it first. Best pieces go to the best customers/mates etc.
Shops sell corals - customers get to see the corals first hand - best stuff goes first. Those in the know - owners, employees, mates, top customers, first in the door normally get first pick.
Importers and shops do not have the room to sit on a massive amount of stock.
It would be nice to have a better selection to pick from but it will not happen. Orders have to be a reasonable size. Importers and shops have to sell down their stock before reordering or the freight cost becomes a real killer.
For the size of Christchurch you are probably better served for marine livestock than the rest of NZ.