Just Like a Johnson M1941 Semi Auto Rifle...maybe a copy of the design ( Multi Lug bolt like an AR15, etc.)
As to getting it into Australiaicon...Do-able (Category "D"; although some states would class it as "R")...Fed. A-G Permission for Specific Use category.

How Much is it (US$ or Can$)?

Make a great Film Gun for Modern/Futuristic Films.

Doc AV