There are numerous road cuttings which have a bit of potential (most are crap though) and there are many old quarries in the Yarra valley heading torards Warburton, many with loose rock. Maroondah resivour l;ooks like it might have something but I am fairly sure that you are not allowed to climb there. Someone told me about an old quarray on the road between toolangi and healsville but I haven't checked this out yet. Maybe you could bind a concrete structure and epoxy some broken bricks on.