Allen VK6XL sends in this report:

An Australian on-line supplier of Aluminium tubing is:

• http://www.hobbytools.com.au     then drill down to metal-tube-round

Thicknesses aren't given, but outside diameters are; 1.59mm, 2.38mm, 3.18mm,  3.97mm, 4.76mm, 5.55mm, 6.35mm, 7.14mm.

All tubing lengths are 300mm.  It is unclear if they are extruded or seamed sections, or if they are telescopic.

More description from VK6XL after receipt of his current order.