I can recommend a US company that can help you make your own since you have a lens in hand to make a mold from. I'm sure there should be local companies in Australia that carry similar products.
Tap Plastics I stumbled across while making some custom items using Plexiglas for my Pontiac Firebird, which is difficult to find parts for due to it's age. It turns out, this company has numerous how to videos on cutting plexiglas, but also on how to make custom molds to make your own parts for cars, models, prototypes, etc.
It should give you some ideas on how to custom make your lens if you don't have any luck finding what you need.
www.tapplastics.com