Rather than drilling them out, I suggest taking a very sharp, small chisel and cutting a slot into the existing screws. Then use a good flat blade screwdriver to screw them out. An impact driver may be able to get them out as well. All you need is one screw, and then you can match it up from a local source.
But I have to ask....why take them out anyway? If they're snug, just leave them alone. It's not like there's any pressure or stress on them, and they cannot back out when the lens is mounted on your camera.