It certainly isn't my training site, I've basically just finished being a student. I don't know much about the running of it, but I think the reason problems are private is because its aimed at training high school students and they want to give problems in a structured way rather than intimidating people with a massive list of them.

This: http://orac.amt.edu.au/aioc/train is the site, you could try asking using the email at the bottom to be given specific problems.