I counter sunk one of the butt plate screw holes on my fowler project a little too wide by not paying attention. A #10 screw goes in a little too deeply and shows the countersink.
I looked locally for any slotted, round head, countersunk #12 screw and came up completely blank. Then I found this place on line:
http://www.blacksmithbolt.com/ They have everything, unplated, every size. I bought a lifetime supply for $7, of course shipping was $11. I spent a sizable chunk of change on fuel going to every bolt and screw place in town on what turned out to be a wild goose chase so $11 for shipping didn't sound to bad.
Just a heads up.