Go to ACE hardware many of them have an assortment of gun screws. Get an 8-32 screw with the correct head. It will be to long, but you can grind or file it to the length of your original screw plus the thickness of the shim.
If you get a couple 8-32 nuts and tighten those on the screw you will have something to hold it in a vise with while filing and when you remove them they will remove any burr from last thread.