Note: In shoulder Bolts if you are going to subject them to side loading please chose either the Holo-Chrome or Unbrako. The imported, although cheaper are usually weaker in shear strength or more brittle and prone to cracking and fatigue due to vibrations. http://www1.mscdirect.com/eCommerce...Ctk=All_MSC¤tMSCtx=mode+matchallpartial
If they wont be subject to heavy duty use like load bearing the stainless ones are a lot cheaper.
For critical hardware and machine tooling I've always liked MSC. Of course there are others out there.
McMaster Carr is good as is Fastenal but with bolts you never know what you are getting (brand, ratings wise) and of course there's always Grainger Industrial Supply.