My father told me after 37ys that I have a half sister. I want to find her but don't know how? any ideas?

I would reccomend contacting some type of agency in Australia first to see what legal ways you can go about locating her. Also, it would probably be good to start posting on various websites about searching for a lost sibling and what information you have about her. You never know, she or someone that knows her may just stumble across one of your posts. A Good place to start would be some geanology websites where people are always looking for things such as this or family connections.