Replacing all of the OEM DISA valves screws costs approximately $45 which is expensive considering they're just screws. Here is an aftermarket alternative.

Includes all the screws needed to install DISA valves on your N52 3 stage manifold. Thread count is greater than OEM screws so installation will feel tighter. 4mm Allen heads, recommended to be installed with socket on a rachet. A small coating of cutting oil might aid in an easier installation. 

4mm Allen heads

Alloy steel

Black Oxide finish