Yeah, there should be like ~16 years of HSC exams around if you want exam conditions. Not a whole lot of schools offer SDD, so I imagine a lot of the trial exams that get done are from some of the external providers and generally copyrighted.
Yeah, there should be plenty of competitive programming questions around for olympiad and ICPC prep. I would say SDD algorithms questions are usually more straight forward than the simplest competitive programming questions, so i'd probably only recommend it for a high achiever starved for resources.