Try this out fit
http://www.fastenal.com/web/home.ex they are a commercial outfit that I've had good luck with. They seem to have a pretty good international distribution system, though I don't see listed an outlet in Australia or New Zealand.
The only problem is generally they only sell in bulk qunatities of 50 or 100 but their prices on grade 8 bolts is low enough that your buying a box of 100 for what you pay in the hardware store for 25.
One heavy equipment dealer near me has put is bolt bins out front in the parts area and sells Fastenal Grade 8 bolts by the pound. (about $4.50USD) I go in and buy bolts, nuts, flat washers, and lock washer taking a hand full or two of each size I need to restock my bolt drawers. I worked out the cost and it comes out that I'm using all grade 8 bolts for lot less than what cheap (quality) grade 5 hardware store bolts cost.
Cheers