Probably if grevillea are available there you will be able to find low phosphorus, but I don't know how easily. I use osmocote for australian natives, though they are getting a little large for that. Cow manure is a possible but poorer substitute. Your soil and conditions sound good if they are growing wild anyway. It dries out a lot here, and though they are commonly known as drought tolerant, they really thrive when keeping the water up to them 2 or 3 times a week. They wouldn't like to be soggy though. They are prone to a fungus and most have a bit of this. I use gypsum to break the clay here and also put sulphur on everything because our bore water is very alkaline.
You are also supposed to cut off the old seed pods to encourage energy into the new flowers, but I am too lazy (err busy..) for that.
Have you tried growing callistemon (bottlebrush) too?
Now you know we'd have to anaesthetize you to feed you the big V!