Hi, I am revisiting this topic as I too am chasing the Australian form of Cucumis melo subsp. agrestis. A few corporations are now cultivating this plant, but obtaining even a few seeds from them is problematic. They covet the seed like it is their own trademark. I recently asked a government run nursery in the NT who told me frankly that only indigenous people can collect these seeds and "anyone else" will require a permit. I have emailed various other people involved in bushfoods, but have met the same dead ends. The fruits are sold in cities like Melbourne, but are frozen so that the seeds are killed.
By the way this species is native. It is definitely also a "cucurbit", that is in the same genus as Armenian cucumbers, muskmelons, rockmelons, cantaloup etc. In fact it is even the same species as these, just a different subspecies and a wild form of that subspecies. The problem is that so much lumping has gone on with Cucumis species worldwide, there is probably more than a couple of species being lumped under the name in Australia. Hopefully one day taxonomists will sort them out. Until then they are unfortunately all lumped in with Cucumis melo subsp. agrestis. It could turn out that we also have wild African forms of this subspecies in Australia. DNA testing may help to sort them out in time.
C. myriocarpus is another introduced African species in Australia with prickly fruits that are bitter and poisonous. We have other exotic species as well.
Considering that Cucumis melo subsp. agrestis is so common in many parts of northern Australia, producing millions of fruits in a good season (as we have recently had), I am finding it very difficult to understand why seeds should be so difficult to obtain. If anyone does have some seeds to share, please let us know.