Hi Mo,
From what I can make out (could be wrong), due to Oz Data Protection Laws, any details such as CV's are binned straight away unless the company intends to invite you for interview etc, unlike in the UK where your details will be kept for 6 months because of the UK Data Protection Act.
Like yourselves, I thought of sending my CV here there and everywhere without necessarily applying for an advertised position. This could be a waste of time.
Re agencies, I posted my details to TAD Technical Careers & Contracts, who specialise in various industry sectors including Building & Construction:
www.tad.com.au.
I did contact various other agencies, but TAD were the only one to acknowledge me and maintain any contact. Worth a try. I was contacted by Nikki Reeves at TAD:-
nreeves@tad.com.au
Hope this helps a little and best of luck with everything!!
Scott.