...I think, but do not know for certain, that those are just the same standard Shimano DT indexing shifter machine screws that come with all their other similar shifters (i.e. not Sante specific).
I use some bolts I got at the local industrial fasteners place here, but they are a little long and I have to shorten them. It's basically a large flat (pan) headed M5 machine screw, but in a specific length that's hard to find without paying extra for the ones from Shimano.