Anyone looking to buy any stainless stuff, (metric only) should consider screwfix.com
I just bought a load of stock and the prices are very keen. they stock mainly A2, which is fine for most apps within the boat, and a limited amount of A4, for the imersed stuff.
box of 100 M8x50 hex A2 machine screws (bolts threaded all the way to the head)=£14.16 inc vat
100) M6x50 as above = £8.24
100) M10 Nyloc nuts =£6.33
100) M6 Nyloc nuts = £1.32
100) M10 S/S plain washers = £1.58
As you can see, these are very keen priced especially compared to chandlery prices.
Navigating the site and finding stuff is a little tricky, easy way is to just use the sites own search feature.
PS. these prices are inc Vat AND delivery!