My Force FD and Red RD are both flathead screwdriver and (tiny) hex key compatable. Look closely and you'll see that unlike the typical limit screw, they aren't phillips/flathead type bolts. It fooled me for over a year.
That said, if you ever need to replace something like this, look up "fastener" in your yellow pages or search for an online site that sells metric, probably stainless steel, fasteners. You just need to figure out the size you want and look for "socket head" bolts and screws. For example: http://www.mcmaster.com/#socket-head-cap-screws/=i2qmi1
" onclick="window.open(this.href);return false;. Problem is they might only sell in quantity, so look locally. I happen to have a couple places locally I can find this stuff and just go there, hopefully with the screw I want to replace, or one similar that i can compare to, and either ask the counter guy or browse. If you're unsure of the size, the easy way is to bring it in to a place that has bolts and find out which bolt it fits.
I haven't looked at the hex socket in the limit screws lately, but they are probably M2.5 or M2? Pretty small.