Hi Oztag
This seems to be a common weakness. I had exactly the same happen to me and I know others have to.
In the end I gave up and bought a box of mixed watch screws from Ebay, it will only cost you a few $'s and more than likely your going to find another falls of another rep in the future. Whilst your on the bay, I also suggest a box of mixed bracelet pins could be useful.
It goes without saying, check the other screws and check any new reps the moment you get them...quality control is mostly 2 letters used in adverts rather than anything meaningful, so don't count on it.