EDIT: Australia Post have updated their page and now have the Write to Santa option:
Australia Post Santa Mail – Let's write to Santa
I can't see anything about them sending a letter back, going to try it and see what happens! Think Santa delivers new boyfriends?
You send the letter to:
NORTH POLE 9999
It's time to write to Santa!
Santa receives thousands of letters from children all over Australia with requests for all sorts of things, including toys, pets and even world peace.
Australia Post works with Santa, and his elves, at Christmas to make sure you receive a reply to your letter (you must live in Australia though).
Gav I've not found a free one for Australia, this American website does print at home ones:
Free Letters from Santa - Free personalized Printable Santa Letters
It has a free print option I'm sure you can find a template online to do this, but it doesn't have the excitement of getting one in the post
A letter from Santa for Kids