Go to a farm supply store. TSC, Big R, Atwoods, QF&F, etc. They will have fasteners by the pound, typically a huge savings in cost and a shorter checkout line compared to Lowes or Home Despot. Almost every one is well stocked with Gr5 & the basics in Gr8. Sometimes they will have metric 8.8 by the pound if you are lucky. And you will feel better giving them your money than at the big box stores.
Ace, TrueValue, Sears HDWE, it depends on the store. Usually they have the plastic bins, but the restocking isn't always up to date.
Autozone is the last place I would go for hardware, although they do have a lot of nuts behind the counter. "year, make, and model" no matter what question you ask them.