There are at least three movies that go by the name "Taboo": the 1980 pornographic version, the 2000 Japanese-language samurai epic, and the 2003 straight-to-DVD horror flick. The last two can both be found in Amazon.com's movie section; the 1980 pornographic version may be harder to find.
If the 1980 movie is so desired, one has to go out of the way to websites that cater to these types of films. The Internet Adult Film Database appears to be the most thorough resource for finding these films and revealing whether or not they're available. Since this was considered "One of the Greatest Adult Films of All Time," it is available online at 12 different sites.