i need to buy aluminium extrusion for a project for my cat and mast section would be perfect. About trailer sailer size. Any ideas where one might look for such things? I've tried eBay and gumtree with limited success. Should I call around marinas or something?
i need about 12m in total 2 lengths of 6m would be ideal.
All Yacht Spars in Brisbane or any mast builder in Sydney would probably have sections in their scrap bin you could buy at scrap price.
In answer to your thread title question, I have to say pretty much any place after a cyclone!! 
But yeah, like Jode says All Yacht Spars in Brisbane should have the juice you are looking for but two 6 metre lengths freighted to you in NSW might cancel any cost benefit.
www.tempospars.com.au/masts.html
Maybe their TS104 is what you are looking for? Not far from you at Brookvale, so worth a phone call for prices of pieces.
If you can't find a couple of masts maybe try
www.ullrich.com.au/aluminium-extrusions/
As you are in NSW I would try Whale Spars
www.whalespars.com/
They are decent people and will most likely help you with your project.
Ed
Thanks guys I think I found the right supplier in the list you gave me. 
The project is a swim platform/trampoline for the back of the cat. Last season the experience of getting out of the water wasn't great for kids and grandparents so I'm trying to make it more pleasant, while also giving people a place to rest when swimming. It also needs to be easily raised out of the water to form a net/pushpit. I get very nervous when kids or pets go near the stern when underway so it will have two jobs.
Using mast/spar section is convenient for strength/corrosion/weight but also means the net that forms the centre of the hammock will attach in the channel. This will be more comfortable for the backs of knees and soles of feet. Hope that makes sense.
get a lillypad pool floaty thing, like what they teach kids to swim on.
we bought one a few summers ago online for the same reason from one of the pool websites
Great for if you want to get wet but not swim, ties easy onto a stern, and is a usefull emergency device.
Makes a step just below the waterline you can stand on, plus just roll it up and store on the boat, or as a cushion on the tramp.
most of all, it's lightweight.
light cat=happy cat
You mean like the one on the back of Aristocat2 ?
perfectnaturecruises.com.au/galleries/
Yep pretty much like that except with a single beam that runs along the bottom edge which would form a step below the water line so people can go from the beam and then up onto the transom.
I tried rope ladders and stuff but it was not very successful. The main goal is getting a step below the water line but I thought I could hit a few birds with one stone.
I'll keep trying to strip weight out of the design
