I buy all my Astro fixing hardware etc... from Bolts and Industrial Supplies , they are a national supplier. prices are ok but not the cheapest. I use them as they have everything in every size and usually in stock
www.bolt.com.au
Melbourne phone number 1300 852 338
I’ve ordered quantities of bolts , nuts , washers both in mild steel , galvanised and stainless as low as 5 of each and they will supply ( but you still pay same delivery charge for 5 or 50 though )
Hope the above helps