Adblue has been used by automakers for a while to reduce the emissions of large trucks. More recently it has become popular as a way of reducing the harmful particulates from small passenger cars being sold in Europe. Adblue is a concentrated Urea solution (strong pee) and is corrosive, so be careful when handling it.
The Mazda CX7 requires the Adblue to be topped up every 20K km's, but sometimes requires filling more regularly. It can be expensive to get a dealer to fill it for you, but if you are a little bit technical, you can easily fill it up yourself. This video gives you all the info you need to find the filling point and fill it up for a fraction of the cost that a dealer would charge.
There are a few large truck stops in each of Australia's capital cities that have Adblue available at the pump, next to the diesel pumps. There are more service stations that sell it in 10, 15 or 20L containers. You may also be able to get it from some auto parts shops or agricultural suppliers. At the pump it's about $1.30 per litre and the Mazda takes about 15L.
All you need, is a phillips head screw driver and a 10mm wrench. What the video and it will tell you everything you need to know.