Nuts and Bolts, Sourcing the right hardware. Options

[Chaznaster]

Hi All. As we dig deeper into our 914, we are finding a random assortment of nuts and bolts that I expect were incorporated into the car over the years. While I am not trying to source original hardware, I’d like to swap the odd ones out to be at more consistent (and, of course replacing any trashed/ rounded over/ damaged ones). Buying one or two at a time is going to get expensive and I cannot find a good reference for the right grade to use anyway (5.8, 8.8, 10.9, 12.9).
Is there a short list of the most common hardware found on our cars that I could use to start a collection of new ones?
Thank You!

[914 RZ-1]

There happens to be a supplier of metric hardware in my town (Metric Specialties) and I would take the old nut/bolt/etc. to them and see if they had it. I also found that a small, local hardware store (in my case a True Value) would often have what I needed. Lastly, the Lowes near me seems to have a better selection of metric stuff than the Home Depot.