Seeds from Australian native citrus

Certainly a Banksia - but what you actually seem to have is not a seed at all, but a dead flower-head, cut before the seeds have formed. I am sure a bit of searching on the internet would find you a picture of a seedhead, for comparison. Trish

The limestone adds an interesting challenge, as far as we Eastern Australians are concerned. What is your pH? Your temperature extremes, of course, are unremarkable to plants of the inland here. However, the rainfall is also a big factor. You may get too much of it, for many of our inland plants. How much do you get, and which is the rainy part of your year? Trish

Embothrium is right-- the sweet-pea-like plant is a Baptisia. I would hazard Baptisia australis- blue false indigo, since that's the most common blue one throughout most of it's range, and used extensively in the horticulture trade. Both sweetpea and the false indigos are in Faboideae, so they are distant relatives.