As Somye said, the problem with the past VCAA papers is that most of it isn't relevant, being based on that year's book of The Aeneid. However, the unseens from the current study deisgn VCAA past exams are still excellent to do under timed conditions.
Furthermore, each year Xavier College produces a number of trial exams (last year there were either three or four in total, if I remember correctly). However, I'm unsure how you would go about ascertaining these; our classes at MGS, for instance, were given them by our teacher, who was in contact with the Xavier teacher.
Other than those, I don't know of any other trial exams which exist, unfortunately! For Latin they aren't too vital though, to be honest, so don't worry too much; it's not like Methods or something where you want to have done lots and lots of papers.