Vince-
Stainless is Ok for light duty/cosmetic uses, but most is either 304 or, in rare cases, 316. Neither one is very strong (~ grade 2 me thinks). I used to buy mine in bulk from MSC Fasteners near Pittsburgh, PA. No idea if they are still around.
Now I buy my hardware in bulk from either Aircraft Spruce or the local Caterpillar dealer. Between them, they have absolutely everything you could possibly imagine. It's either yellow cad plated or black oxide and is at least grade 5, most is grade 8.
A few years ago, I went to visit my in-laws in Dayton, OH. We dropped the wives/kidlets off at some mall and spent the entire day at Mendelsons (sp?) - same family that runs Hamfest. Oh man, what a paradise... they sell hardware by the pound - like 50 cents/lb as I recall. The place was just unreal, imagine six or seven floors each the size of a Home Depot filled with surplus harware/electronics/whatever. It was pure heaven. Sadly, I heard they are closing/moving.
Look around eBay/Amazon for a cheap copy of Carrol Smith's book entitled Nuts, Bolts, Fasteners and Plumbing. It's a great reference.