Me three. I found this site (I haven't used them before, maybe someone else on this site has?)
http://herbalistics.com.au/product/terminalia-ferdinandiana-kakadu-plum-seed/
They sell the seed. 4.95 for 5 seeds. Plus postage. They are closing for winter soon.
The plant sounds like it might be pretty hard to start from seed, but hardy once established, which is why I hoping to find someone who was growing it locally. It would also prove it grows down this far south...not sure about Melbourne though, but would be interested in your hothouse project.