There is a North American variety which should grow in Southern Victoria. You can get seeds here (I have) : http://www.ebay.com.au/itm/Annona-Custard-apple-fruit-tree-types-Many-Rare-Yummy-Easy-grow-U-pick-Seeds-/231692684797?var=&hash=item35f1f5cdfd
Other sub-tropical fruit which are thriving in our garden: Black Sapote, Mountain Paw Paw, Guavas (Cherry, Coastal, Chilean), cold climate Bananas (eg Lady’s Fingers), Monstera Deliciosa, Avocado…we aim to eventually have representatives of every edible and useful plant that will grow in Southern Victoria – but now, off to the garden!