Sorry, I noticed that too after trying to look around on that site...the don't seem to really have their shit together, huh? That was just the first one that popped up when I searched...
Like dwalmop says, I too suspect the GTO stuff would work, but I'd be wary of differences due to emissions systems that your model may not be comparable to ours...I know the Aussie Holdens are very different in many respects because of that...
I know the stuff is out there, because it's a popular car in Arab countries, so I'm sure there's an aftermarket performance market for it...finding it may prove challenging...
Your best bet if you hit a brick wall might be to email Holden AU directly and ask them if they can tell you anything....
I'm still curious, where you live, is it badged as a Chevrolet?
Here's a link that actually has performance parts for LS-1 Holdens...maybe see what they can tell you...
http://www.capa.com.au/ls1_engine.htm
I'll keep looking in the meantime...