We're near Melbourne, but my son is 14, so probably not a good fit. Have you tried hooking up with the homeschool groups in the area? I know "Homeschoolers and Friends" accepts families who are homeschool-friendly or "afterschooling" as well as homeschoolers, and there are at least one or two gifted kids in the same age range as your DS there.

PM me and I'll set up introductions if you are interested.