There aren't any standards for miniature screws. The screws are custom designed to the application. I am sure that Rokinon uses the same screws in many of its lenses, but those screws won't be the same as those Nikon, or any other maker, uses.
If you do a lot of repair it is worthwhile buying up non-working cameras to strip for parts like screws. Often you can find a screw or fiddly bit that fits well enough even though it isn't an exact fit. It's like going to the junkyard to find parts for an old car.