you can get them at pretty much any art store, Michaels, Aaron Bros, Blick etc. or you can order them online. They are moderately expensive (about 1.50 - 1.99 per pencil) but worth it if you are wanting to do some colored pencil work!
I found this list of art suppliers in NZ, I don't know if you live near any, but it's a start. I bet almost all have prismacolors. You can also find them on ebay for good prices, or www.dickblick.com; you gotta get some!
AQctually this was my first prismacolor drawing that I did....They are just amazing. I didn't really know much about how to use them well they just work really nicely if you get creative!