They're a bit tougher in higher grades, but even then, they're not as rare or as valuable as their catalog values imply.
When I was trying to collect everything I paid particular attention to NZ because it seemed more attainable than most. Coins start in 1933 and there are really no impossible coins
It's been awhile since I did it. I know some of the coins around the World War II years have smaller mintages but there aren't really any that get into the big bucks besides the 1935 threepence unless you are looking for high grade. I was always just interested in filling the hole, not finding the highest grade possible. Now looking at the catalog I see there is a 1935 crown with a mintage of 660 that I do not have. But besides that the rest are pretty much attainable.
So I got a few more New Zealand Coins that I had graded from Anacs. Three of them graded as really High Proofs. Check these out: PF69 DCAM 1993 Dollar graded from Anacs! When I sent this out, I had no thought it would grade this high, but you have to LOVE the KIWI here. It just leans out of the coin.
When I saw @Hiddendragon post his slabbed 1935 3 pence I had to go look at my raw ones. Mine is but a year removed from glory. Edit add: Numista says Two carved patu (Maori short-handled clubs)
Hey, I have more! I just poked through my world trips coin jar. Some of these must have been circulating in Australia as I have not been back to NZ since 1985.