There is a company that makes high quality bolts, nuts and studs for performance cars and racing teams, which is also highly sought after by the aftermarket hot rod and muscle car industry:
https://arp-bolts.com/
On page 21 of their catalog (top right of the home page), they list the requirements for custom dimensioned bolts and studs. ARP are NOT hardware priced bolts and fasteners, but they are reasonably priced for the high quality items they are.
https://arpcatalog.com/20/