Am I better off to get my truck license in NZ or Perth, and does anyone know a good webpage to source about it?

Try the Perth government website. They should have a Motoring page that can help you. Usually, whatever full licence you have have in NZ automatically results to the same equivalent in Aus (and you usually don't have to sit a practical test over there - just eye test and show your NZ licence)..so I would recommend doing it in NZ then transferring to it over there - but double check with the government website and e-mail them to be clear. Good luck.