Correct on the M3x4 screws, and they can be found at home hardware box stores in Allen head versions. They will do fine, I recently picked some up at The Home Depot. Torx head variants can be found at Fastenal. Be careful with stainless into the alloy of the sight, IIRC, they can gall up. DO NOT pay $7 a screw; I've read that Aimpoint will send you what you need if you ask.
BTW, there is a version of LockTite for small fasteners, it's purple, I've taken to using it on optics.