Look up Chapman Tools, I’ve used their tools on minor gunsmithing projects. Excellent quality, made in the USA, and reasonably priced.
I have a set of their gunsmithing screwdriver bits too.
Here is an interesting application:
I am working on a postwar 2340 GG-1 with battery damage. Some of the battery gunk leaked onto the power truck on that end, and fused the side frame and its mounting screw together. I put the truck through multiple trips through an ultrasonic cleaner, and then kept the parts wet with a rust breaker for days. The screw still would not turn with a standard screw driver.
Finally I got out my gunsmith set, and picked a bit that was almost an exact fit for the slot. I had to be slow and careful, but the screw came right out.
By the way, I think screwdrivers and driver bits are one of the tools where it pays to buy good quality. Cheap ones often don't fit the screws well, and can damage them as they self-destruct