My parents were granted a 3 years visitor visa, but idk how since we didn't even apply for a multiple entry or mentioned anything about wanting a 3 years visa. But no, that's the only subclass for a visitor visa : subclass 600.
You know 12 months is good enough if granted. Which form to submit ? Really? You know you can google it and it's everywhere. If you want someone to spoon feed you, you should hire a migration agent.