You can get rice bubbles (or rice krispies) from a shop that sells bulk goods here, you just spoon them out of a bin into a plastic bag. That works out to cost about half the price of what you'd pay if you bought a packet. I have lots of plastic cereal containers that my daughter bought and I just keep filling them up.
The chocolate rice bubble thing (I'm not sure what it is actually called, but it has been around for ages as I even remember my own mother making them for us) is easy to make and you can do it in half an hour or so. The longest part is melting the chocolate.
You just get a block of cooking chocolate, or actually any chocolate with a high cocoa ratio will do, and melt about half of it in a pot on the stove, when it is melted add about three table spoons of icing sugar, put it in a mixing bowl and add hydrogenated coconut oil - I think it is called copha - (or any hardened vegetable fat will do) - about 6 or 8 ounces, also melted and then chuck in (I say "chuck in" because I've never measured the quantity - maybe 2 or 3 cupfuls, some rice bubbles (or krispies) and lightly mix it in. Put a spoonful in each of about 12 or so paper cupcake cases and leave to solidify over night or for a few hours, in the fridge.
They are really yummy. My mother used to put in desiccated cocoanut and coloured sprinkles but I don't like cocoanut and I don't really have a "sweet tooth" so don't want the added sweetness of sprinkles.
I don't think this is any way a NZ thing. American kids probably have had them for generations as well. I just think they are a staple at kids' parties along with the little saveloy sausages and tomato sauce and the cookies with icing on and the cut up oranges. Unfortunately the art of making food for kids' parties seems to be dying and more and more people are opting for McDonalds food for their kids or pizza.
Having young kids for the second time around (grandchildren) I am starting to feel like a (as my grandson puts it) dinosaur. I make all these things for their parties now, but at their friends' parties, everything is bought and they don't even have fairy bread.