Ed Byers does ship to Australia. I bought four of his drives a couple of years ago. He just doesn't include the overseas shipping segment on eBay as it is a hassle for him.
His email address is
erbyers@san.rr.com
Tell him what sizes you are after and he will let you know if he has them in stock or has a size close to it. From what I gather he is no long in large scale production and is slowly selling off his stock.
He can bore the drives to your exact measurement and you need to decide if you also need clutches.
He sells two types of worm. The cheaper is a spring loaded version mounted at one end. The second is the more traditional worm mounted at both ends. This version is also more accurate. I get an accuracy of 4.5 arc sec peak to peak without PEC.
