I taught my son a little when he was around 18 months as he wasn't talking yet and he was getting frustrated, so that helped a little. Mostly we used the word 'please' more than anything else, and 'drink' when he's thirsty. He picked up other words from action songs like spider, star, worm...pretty useless but cute heheh. Only helped when there's a spider or millipede in the house that he spotted. He started talking soon after so we didn't pursue sign language further.
I've only heard of this organisation that has DVDs, books and flashcards: Baby Sign Language Classes and Products Using Auslan | Australian Sign Language For Babies not sure if they post internationally though. It's good to start young even when they dont't look like they understand. They probably are absorbing everything