When I used to run matches....
I used three 'sources':
1. Replication of an actual event, like the CHP shootout in the early '70s; or the recent attack on the church meeting in Chicago. Also, replication of actual circumstances that did not result in deadly physical force, but might have done. Sort of a 'what if' game.
2. Replication of a movie scene. I once used the final shootout in "The Shootist" for a cowboy stage.
3. A 'test' of a particular skill or skills. The "El Presidente" stage is a test of multiple target acquisition and reloading ability.
Look in the various news agencies for scenarios. You will have to clean them up for safety (unless you have a range where one may shoot 270 degrees...) Use props; chairs, desks, walls, whatever. Not to be discounted is a small task prior to shooting, like turning over a paper to read a number; that number being the first target to shoot in a series.
Avoid thirty round bursts and multiples reloads.... thanks...