Can't help you with Sydney nurseries, Otto, but can suggest you ask your local nursery to order one for you. They probably won't have heard of it before but, once they they have an order for it, they'll ask their suppliers. (Given the drought and downturn in business, they're generally quite obliging these days.) My understanding is that grafted plants have superior flowers to seedlings, but this makes them more expensive. You might want to specify that the plant has to be under a certain price range (eg $25) to avoid being saddled with something very large and expensive.

Cestrum,
Thanks for your advise.

Otto.