Sure that's not a form of D. natalensis?
I have some plants grown from seed labelled as D. madagascariensis from Mpumalanga that look very much like this plant.
You keep it dry. Bone dry.
For more control I'd place it in a ziplock bag in a cool place indoors and let it do what it wants. When it begins to grow repot and water. If you're lucky it'll hold back until next autumn.
All of the forms originating from southern Australia, ie- Victoria, Tasmania, South Australia and WA fork only once. I'm surprised they appear to be so uncommon in cultivation in your part of the world.
I think that you'll find that the import requirements for other countries vary from those of the US. The US is the only country with the small seed lots permit.
I won't dispute that. I've grown a number of forms and clones over the years and have only ever managed to produce seed when I have manually crossed different clones. I guess there must be some other clones that will occasionally produce a small amount of seed without any help.