Brett Hoby Parts did have some worms on display last time I was in but I'm pretty certain that they don't have the gears in stock. Minature Bearings who I think supply that stuff to them are in the same building but I don't think that they do retail (and both are a long way from you).
I've seen printed catalog details on worm gears at Bsc
http://www.bsc.com.au/html-bsc05/indexBSC.htm which they can get in. I think that had to come from overseas but they can get worm gears, from memory the multiple lead gears available were low ratio. I could not find anything in the online catalog.
I've taken a break from my hobbing attempts for a while as I do some other stuff but if I don't decide to buy an EQ6 and continue building myself I suspect that's the way to go. Hobbing the gear seems to be the easy bit, getting the rest of it machined properly has caused more trouble.
Bob