A large magnet can help retrieve small screws like that. And inexpensive TORX screwdriver sets can be had at Harbor Freight Tools... many different sets for under $10... way under for some.

For front sight installation there are links by members and great care must be taken to make sure the sight is seated correctly and that the screw is too low for the barrel to strike it in firing... the major cause of front sight failures on the "C" models.

Wynn