Bolts in bulk? Anyone done this? What sizes?

I agree with most of the above.

Buy a parts car :) I suggest a 5th Ave.

You will get hundreds of dollars in OEM Mopar USA made bolts.

I also strip bolts from cars in U pull yards. At least all I have the patience to get.

Even 80's and 90's FWD cars have lots of correct for 60's and 70's car bolts (although the machining logo on the bolt head may not be the same) I'm using 86 Daytona bolts to hold the luggage rack on my 67 Wagon.
Lot's of places will just charge a couple dollars for a coffee can full.

I pay particular attention to oddly made bolts with non-standard lengths and shoulders.
Water pump and alternator pivot bolts are a perfect example.
I get the spacers from the alternator, too.
.....and the speed nuts from various places on the car.
Those are also different OEM than aftermarket.

I'm also amazed these are often discarded after being removed. Score for me- all the work is already done.