The only shooting that plausibly seems like it could have been a false flag was the Port Arthur shooting in Australia. Seriously, read the official version of what happened and none of it makes any sense.
A mentally retarded man with an IQ of 66 and no military experience whatsoever somehow kills 18 people with 18 headshots in the span of just a few seconds firing entirely from the hip with his non-dominant hand, all while manually counting rounds at 50+ rpm in order to tactically reload with a round still in the chamber? The only two police officers on the entire island were away on a wild goose chase at the time of the shooting, called away to investigate a stash of heroin that turned out to be soap? While Martin Bryant was on the phone with the police during the hostage standoff, several gunshots are heard coming from his position indicating a second shooter, which were recorded on the transcript as coughs? Yep, totally nothing fishy going on there.
It's also one of the only shootings that led to an overwhelming change in legislation, which makes it all even more suspicious (despite what the Aussies would like you to think, plenty of mass shootings have happened before and after Port Arthur).