Ummm, I assume you want this for JO, as JA has plenty of double-bladed lightsaber action. A lot of MP mods for JO allow you to use one, or you could create your own server and type in "thedestroyer" into the console window. Unfortunately, there is no way to get it to work in SP as Raven has not (and probably never will) release the source code.
Or maybe you just want a Darth Maul saber hilt. If that's the case, go check out the websites that Big_Boss mentioned.