I make most all of the screws needed for a project. I look at it as part of the building process.
I make the wood screws too, but use a machine screw thread and usually a counter sunk shoulder head instead of a plain V shaped counter sink as on a common wood screw.
The machine screw threads hold great in hard woods like maple. A #8 is the most common size I use for trigger guards, toe plate, etc. Sometimes a #6
Butt plates may use a #10.
For long shanked screws like lock bolts and tang screw, I often make the head and shank separate. I drill a blind hole on the bottom of the head, hard solder the shank in place and final shape and square up the head as one piece. Then thread as needed.
Sometimes I make them as one piece. Depends on nothing at all in particular at the time. Just how I want to make it.
I have a small JET lathe and it works well for the projects.
..and CRS for the screws works fine too. Plenty of that around in many forms and diameters.
I use a jewelers saw to cut the slots. They can be widened if needed either by double cutting with the same saw blade. Or simple filing the slot wider. Opening the slot to the old style V shape is easy to do also with a very slim needle file.
No need to depend on a parts supplier for screws.,,and they don't take much time.