Just happened to be in Ace Hardware this morning and checked their screw inventory for suitable intonation-lockdown replacements. The machine screws you need are, in fact, 3/32"-48 but will be designated 3-48. The shortest ones my local Ace had were round Phillips head (not round slot-head) and 1/4" long, so you'd have to cut them down to 1/8" if you want the tips to be flush (which, in practical terms, isn't really essential) under the bridge base plate when they are tightened down. If you want to shorten the length of a 1/4"-long one, put a nut on it before cutting, then unscrew/remove the nut after you cut. The reason for doing this is to clean up any thread burrs created when you cut (so you won't bugger the female threads of the intonation sliders when you try to screw in the replacement screw). Shortening shouldn't be necessary because it's doubtful that you'd ever have to set your bridge height so low that the screw tips protruding underneath would ever create interference.
If you want exact replacements, you might try Fastenal or McMaster-Carr online, but they may only ofter them in quantities which far exceed your needs.
Again, all of the above pertains to a current-production, Newark Street Starfire bridge. You'll have to double check to make sure that the same spec fasteners were used on you older, JS bridge.
