I don't have, and haven't looked for, a source on that subject. That's why I said 'apparently'. If I find one I'll edit this and add it in. Otherwise, assume that I was misinformed and blargleblarg. :3
EDIT Okay, apparently they do exist. And in quite a few numbers. The Aum Shinrikyo was based upon Buddhist teachings. Through history there have been numerous Buddhist warriors who 'purged' the land of certain factions. Lots of stuff. There's even actual teachings of violence by Buddhist doctrine, according to the Wikipedia page.
There's probably more specific articles available, but Wikipedia tends to have them all in a big compendium. And Wikipedia makes you automatically right in debates because that's how debating works. Cite Wikipedia. Get money. :D