Oh wow that's ages away, you've got heaps of time still
I don't have any practice SACs - some of the trouble is that because it's new, there's not many in circulation yet. The other is that most SACs are copyrighted materials so we can't go passing them around anyway.
DLTV has practice SACs and exams available for purchase but it's aimed at schools, not individuals, so you'd have to sucker your school into buying it for you. Definitely suggest having a chat to your teacher about what they can work out for you though.
I had the same trouble - it's very easy to say that two systems are dependent on each other, but it's harder to explain why in a precise way. My SAC last year was based around an external roll marking system (so COMPASS but with a new name my teacher made up
) and the state database (I think it was CASES). Another example of dependent systems in a practical sense are record keeping between departments of a company - a car company might have a sales department that sells you the car and collects your personal info, but also a maintanence department that reminds you to come in and get your work done. Thinking about these (and even coming up with your own) might be the next best thing to having a practice SAC, since it's these sorts of relationships that the SAC will be about.