Ah a hand change Vintage rider. My father had a Model P. His had the asbestos rope front brake! Utterly useless. He now has a 1930 Model NSD. Theres pics of it somewhere in my albums. I'm assuming your bike has a brass lever for the throttle and not a twist grip. These old bikes take some getting used to don't they? But once you do, 40mph is as much a blast as 140 on a sport bike. Happy riding.
As for parts you might struggle. Over here we have the Vintage Motorcycle Club which can be a good starting point. Here's a link to their page.
http://www.vmcc.net/
Dunno what the oz equivalent is.