Almost all the bolts on these cars are standard US/English (as opposed to metric) sizes. Most of the bolts are fine thread, but there are a few coarse thread ones. I use pretty much all grade 8 because it's not that much more expensive than grade 5.
Find a hardware store that has a good selection. I don't find that the big box hardware stores have enough selection, and they often offer things in prepackaged quantities. You need to find a hardware store that keeps the bolts, nuts, washers in little bins so you can buy as many or as few as you need. They're also cheaper that way. Ask around if you don't know of place in your area.