I want to make blocks of to fill a foam enclosure to practise jumping
motorbikes into. How do i make the foam? where do I source the
ingedients in Australia?

I assume that you are talking about the soft foam blocks. These are
polyurethane foam blocks. They are equivalent to Sofa cushion
material. Whilst the chemistry is fairly simple It is not that easy to
make nice consistent blocks on your own. You can buy all the
ingredients on the open market. Most consist of a part A and part B
pack that you need to mix together. You then need some moulds to puor
it into whilst it cures and sets. A good starting point is www.pfa.org
 Whilst this is American it has links to the main suppliers. From
there you should be able to get a local suppliers.
Alternatively try "polyurethane flexible foam australia" within
Google. It brings up a few more related links for Australia