I've never tried to use a TD screw on a Krag, but I'm fairly sure the THREADS are identical. I looked at one of those ads - think it says something about emergency? If that is the one, I believe it was some sort of Bubba-fix, like my brass suggestion.  :-)

What one really SHOULD do is go a legitimate parts dealer (there is a good list at trapdoorcollector.com) and buy the proper screws, even if they are $10 (or whatever) apiece.
It is not like they are totally unobtainable.

ABSOLUTELY NO promises as to when, could well be a year or more, but, since I am about done collecting, my 40-year stash of spares should probably be distributed around. Having said that, I do NOT think I have any Krag sight screws.