There are lots of ways to do that. My authors, Darrel and Sally, have these suggestions.
1. If you are at school, or if you know someone who is, order through the Scholastic Book Club.
2. Go to your local bookshops. If you can't see the titles you want on the shelf, ask the assistant. If the assistant says the books are "not in stock", ask him or her to order them for you. You will need to quote the title(s), author and publisher.
3. Go to an on-line book shop. There are lots, including Booktopia (at http://www.booktopia.com.au ). If you order through them, they get the books from the supplier for you.
4. You can also telephone Scholastic directly and order the titles. (There is a small packing fee.)
5. You can ]order through Amazon, but you need to be careful as the UK editions have different covers and different titles. Read the blurb to make sure you don't order the same book twice. There are French Canadian editions, but the two US editions and the English-language Canadian editions are very much like the Australian ones, and have the same titles and covers.
6. Bolinda Audio ( at http://www.bolinda.com/aus/ ) have the first few on CD - they're ace, and not at expensive as most audio books.
7. Try eBay!