ninja use ninjatos actually not katanas
Nope, that's the hollywood invention. The closest thing to "ninjatos" that would have existed in japan was the chokuto style blade before the advent of clay technology for differential hardening of the blade.
Oh, and also OP, even if there isn't I am making a mod for some. So if you are on PC, you'll be getting some shortly after Skyrim is released. Thus far I have modeled and unwrapped a tanto, a wakizashi, a katana, a chokuto style blade, and a kogarasu zukuri style blade (kinda like a double edged katana but the second edge starts ~1/2 the way down the spine).