Jas, I think if you could procure the proper parts, then a good smith could put it together. What the restrictions on importing a barrel, bottom metal and such to Australia.
The bottom metal,stock and barrel would not be a problem.
Finding and importing a clip slotted reciever would be, the reciever is considered a firearm. Clip- slotted recievers are as rare as hens teeth over here. Most people do not know what you are talking about let alone seen one.
A good smith should be able to machine the clip slot if he had pictures and specs to work with. Where you at anyways, have an Uncle whos been in Canberra since 69,
Have you tried shane clancy in NSW? if your not in a hurry you could try John giles of PSECO http://members.optusnet.com.au/johnhgiles/index.htm, or even send wild bill a pm on here, he may be able to help you out.
Try the M40 build thread, bucketloads of good info for period accurate builds.