hi sflack,
The best kind of aloy boom has to be the ones made out of ergal aluminuim, its the strongest alloy, and it cant be stiffer/stronger than the cheeper carbon booms,
I use tecnolimits ergal King, its brilliant, had alot of hard treatment, been over extended, and anything els you can think of, and still going great!
but as oyu said not that available over the net. and also not the cheapest either,

if you contact windshack they may be able to send interstate, but not too sure.
just look out for ergal alloy, i dont know anyone but technolimits who use it, But i dont know that much anyway

.
check out windshack though
http://windshack.com/products.php?cat=windsurfing&scat=7&id=53 (scroll down to 100% ergal)
good luck