Hi honey, have you tried rice milk, you should be able to get that in Oz. I would reccommend brocolli and other dark green veg, even onions have tonnes of calcium in. There should be enough calcium in his diet if you eat lots of different veg, like nappynutter said you really don't need dairy to fulfill your needs. I know a few vegan mums with very healthy vegan kiddies, so please don't worry. Are you excluding soya completely? Tofu and the soya yoghurts have added calcium so you could use them too. I don't know how old your LO is either but Quinoa, a grain, is a great source of calcium and protein, could be worth a try.
Hope that helps, also have you contacted the Australian vegan society? They are really good too.