Ace IS the PLACE.
6-48 x 1/8" blued set screw.
Look/ask for "gun screws".
They have 6-40, 6-48, 8-40 blued gun screws in a variety of lengths, styles (weaver oval, fillister, slotted, phillips, socket, torx) including slotted set screws.
I just got a set of tip-off rail screws in torx (t-10) in weaver-oval for my Weaver TO-9M rail. I did have to get them 3/8" long and cut them back to 11/32 but when done they apply a LOT of torque with no slip and I dialed mine flush with the receiver for maximum thread engagement. Unlike the slotted oval screws that come with the rail the torx oval are FLAT across the top and don't stick up to touch scope rings. Perfect. Normally, I file the rounded heads of the Weaver supplied ovals flat/flush but the torx don't need it.