Where do you audition st trinians 3?

There is no St Trinians 3. The St Trinians franchise consists of two films:

* St Trinians (2007)

* St Trinians 2: The Legend of Fritton's Gold (2009)

Therefore, there are no auditions for a St Trinians 3.

If you're interested in acting, you should look for opportunities in other films or theatre productions.