It is natural for a nursery to be coy about their sources so that you as a customer don't bypass them and deal with the supplier, although the supplier would likely be a wholesaler that doesn't sell to individuals. It is no surprise they would want you to wait for their stock to arrive. If the expected trees do not arrive as scheduled, try another nursery.

Although many of your questions do not depend on the locality, be aware that this forum gets maybe one posting a month from Australia, if that many.

Good luck on your fruit tree quest.

I was born and raised in Melbourne -- a great place to live, and a great place to grow fruit. As Larry says, most people on this forum are in the US, as I now am. I believe a very well regarded nursery in Australia is Daley's. You can find them on line. I know that here in the US serious fruit tree growers order their trees on line from nurseries that specialize in fruit trees, rather than from local nurseries whose employees tend not to be very knowledgeable about growing fruit trees. And if you want to grow fruit trees, get yourself a copy of the great book by a fellow Melbournian, Louis Glowinski, "The Complete Book of Fruit Growing in Australia." He used to grow an enormous number of kinds of fruit trees on his quarter acre block in Caulfield -- maybe he still does.

I second that book recommendation, and I have a copy.