I can't find any other stories about a squirrel gun being used to stop a rampage at a school. I did find one about a school shooting in Springfield, Oregon in 1998. It said that one kid shot and wounded at least 25 students before he was tackled by other students. It makes no mention of anyone using a gun to stop him.
In The Bias Against Guns, John Lott showed how 98% of the stories used the word "tackled" and did not mention a gun when reporting the Appalachian Law School shootings. I wonder if this is the same? I will try to remember to go back and look at it to see if this one is mentioned, too.
I do remember that shooting at the law school. It wasn't plastered all over the news like the VT shooting, probably because it was stopped for the most part. But also because it had a gun being used to stop a crime.
If you look up the Wiki entry on the Appalachian Law School shooting, they give "conflicting accounts" of what occurred. Just try to follow the sources on the "he was tackled before he could see the two guns" account. Sometimes, I think Wiki errs by trying to include too many "points of view." I highly recommend John Lott's book, The Bias Against Guns, to anybody interested in the subject. Lott interviewed not only the participants, but the reporters who later lied about it, and their editors. Their responses are interesting, to say the least.