If they the two small d/T'd holes, about 1/2" apart, in the rear upper left receiver wall, they should be the receiver/peep sight prep holes, normally plugged with short 6-48 plug screws.
Most gunsmiths worthy of the name should have a drawerful of them - take-offs from rifles they mounted scopes on for their customers, and available to you for next to nothing.
If you need what looks to be a large screw, further forward on the same side of the receiver, it's the "link pin stop screw" - available at
www.wisnersinc.com
.