Here's some info that might help you:
I took the screws off of my Bayard and, as best as I can tell, they are M3x0.6 thread (a metric standard size), the shank diameter is .105", the head diameter is .196 +/- .001, the length of the threaded portion of the shank is .132" and the thickness of the screw head is .070 +/- .002. The screws on my example are cheese head screws, i.e. they are flat, not domed. I have no idea if they are the originals or not, as the gun has some WW I German unit markings on the rear grip strap, and might be German replacements for all I know.
BTW, I have ordered several pairs of grips from those folks at Vintage and the quality is excellent. When they arrive, they will be shiny, but if you dull them down a bit with some Walmart Tech carb cleaner, you will be hard pressed to tell them from the original.
One thing you need to bear in mind is that they use a real pair of grips to make molds from and the repros will have any and all faults that were on the originals. Some of these grips are relatively uncommon and you can't always find the best examples to copy.