Double-edge katana are rarely found in Japan’s history. There are several treasured ones, but most of these types of swords today are replicas from various more recent fantasy and anime sources. In case you come across it, double-edged katana are called Kissaki-moroha-zukuri.
Having a sharp edge on both ends of the blade doesn’t really serve a real purpose on a samurai sword. In fact, it makes the blade less resilient. One thing you should also know is that with a double-edged samurai sword you can’t sheathe it in the traditional way without looking and being extra careful.
Despite the above, if you truly want to own a double-edged katana you will be able to find some below.