Hey Brittany -
Welcome to the forum! To answer your first question, there are a variety of sources to get photographs.
1. You can print them out yourself. Just purchase photo paper and print them out on your computer. You can search for high resolution photos using any search engine. ex. Google. But I wouldn't recommend doing this unless you have a good printer.
2. Purchase photos from sites like All Posters. This is the more expensive option, but if you want high resolution, good quality photos, you may want to pursue this option.
3. I don't know if this option is available in Australia. But you can go search online and find high resolution photos. Save them to a disc and bring it to a photo store. Some stores, (at least in the USA) will take the disc and print out the photo for you. This is less expensive than option 2 but better than option 1.
Now for your second question. Unless you have stamps from the country that you are planning to send your request to, you can't send a SASE. For example if you were sending a request to the USA, you would need to have US Stamps to provide a SASE. You can't provide Australian stamps because they won't work in other countries. So what you should do is go to your local post office and purchase IRC's (International Reply Coupons). They are vouchers that can be redeemed for stamps in any country around the world. Provide 2 or 3 with your autograph request and include a Self Addressed Envelope (SAE). Hope this helps!
Good Luck and Happy Collecting!