Are you looking for a situation where there was an actual shooting, or will the threat of shooting work. (The situation was resolved before any shooting actually took place.) Also, how fresh does the situation need to be?
I ask because I know someone who was a bystander (student) in an incident where a student brought a gun to school and was threatening to start shooting. The incident probably happened somewhere between 6 - 8 years ago. I don't know what kind of information she could give you besides as a student dealing with the fear. I know it is still there for her as she just told me about it recently after my daughter went through a bomb threat at the same school.
Of course, I don't even know if she would be willing to talk.
I would be hesitant to ask her unless the scenario meets your requirements. Feel free to pm me.