Hi Rob,
A lot of places in Oz sell tubes. Here is one example of a place that will make custom tubes.
http://www.telescopes-astronomy.com....es036.htm#tube
I did a quick search for you and the more popular Astronomical suppliers in Oz also sell them ready made.
You can also go to sheet-metal workers and they will roll any size tube you want. You get to pick the material thickness (light, heavy, etc.), Aluminium, colourbond, Gal etc., the colour, length, diameter. Most don't charge a lot for a quick 'one of' job using a small amount of material. They could possibly roll tube rings at the same time to match the diameter.
Hope that helps, Rocker-boy!
