Hi Jo!
Unfortunately we're a bit out of luck when it comes to art supplies... I buy almost everything specialised from PaperInkArts, because it's cheap and their shipping is good. However, I do know a couple of places.
My first point of call is WestArt Supplies in Footscray, Melbourne. They do not have an internet presence (and were quite stern when I asked innocently if they had any plans!) but the owners are really lovely people in spite of that quirk. You can ring them and place an order over the phone, and they're happy to tell you what they can and can't do. They are the only art store in Melbourne I know that has an actual calligraphy section and our particular toys! Lots of nibs, lots and lots of inks, lots and lots and lots of paper. They have automatic pens and gilding supplies and embossing tools and so on.
Melbourne Artists Supplies also has a lot of calligraphy supplies, although not as wide a selection as WestArt. They are in the CBD and I don't know what their mailing policies are but I'm sure they'd talk to you!
DeansArt has a few branches in Melbourne. They don't have a lot of calligraphy-specific toys but they usually have a handful of Speedball nibs and holders, and they are good with gouaches and paper.
Eckersleys you probably already know of!
I hope that's a little bit useful.