I attended Dux College for year 12.. and they are really good - reasonably priced $25/hr.. provide notes and great teaching + homework marking.. so very comprehensive.
But in all honesty, for preliminary you shouldn't be too worried. I slacked off really badly in prelim and managed to get a decent HSC chem mark.. because prelim marks don't carry on to the HSC, and actually the content for HSC chem only uses a few prelim concepts.. which can probably be learnt in one 2 hour lesson or so. But it's up to you.
If I was you, I'd probably save my money and then invest in either a private tutor or a tutoring college for HSC year, or you could invest in a private tutor - maybe late year 11 to accelerate through the HSC, because at the end of the day year 11 doesn't mean anything.