Hi Bronwyn,
These are just powdercoated metal profiles. Readily accessible through your joiner or off the web. These particular ones are 25 x 40mm and 40mm square angles.

When you say off the web, is there any where that you can guide me to?

Sorry, another question. Is it bolted to the floor, i.e., cement slab?

Hi Bronwyn,
There are heaps of companies around so you might want to do a google search for 'steel angles' so you get somewhere that is close to you. A couple of suggestion that are Australia wide:

http://www.orrconsteel.com.au/products/hot-rolled-structural-steel/structural-angle/equal-angle

http://www.jsteel.com.au/contact/

The design in the picture doesn't require any bolts because of the weight of the joinery unit attached. If you are planning on just steel legs with no cupboards you will need to consider bolts and/or larger square angles. The manufacture will be able to help with this choice.