I looked in my TR3 factory parts book, and they list the screw as YJ2182. Translated, that means it's a Parker Kalon "J" Type...sorta like a sheet metal screw without a point. It's a #10 - 1/4" long with a round slotted head. That's the best I can come up with. I have several different stanchions here, and a couple of different types finish pieces and nothing seems to make sense. I took the best two stanchions I had and left the finish pieces off. Didn't seem to make a difference.
Try to see if a short #10 sheet metal screw goes in the holes.