I dont know anywhere in australia that sells RPM stuff and that was the first place i though of. Maybe just buy a nice motor for cheap or something and get the rpm parts with it then you cant complain about buying overseas.
Aluminimum is strong, but also heavy and especially on something such as my savage, id rather have the stock plastic as it flexes and bends itself back into shape whereas alu parts just bend and stay bent until you unbend it with hammer or a similar tool.
Get RPM from tower and it will be well worth it. Its also a LOT cheaper than alu parts.