Order a custom piece of acrylic or some other such material, then shape it through various means, which would be whatever your preference is. Once done, flame polish or buff it with a powered buffer tool.
Personally, I'd just cut it down to the basic shape you want and then sand it down the rest of the way using progressively finer sandpaper until you reach the point where you can start to polish it by either flame or with a buffer of some sort or another.
It's going to be rather expensive however you look at it, I think. Let's say you go with normal acrylic, just extra thick and custom cut. Measurements would be what? 3 inches wide by 24 inches long and 2 inches thick? It would cost you $80 + S&H. That's pretty much the cheapest I could get it, too. Just a bit more here and there and it really jumps up in price.
Edit: Using Google Image Search, the sword doesn't seem to be crystal clear. Is this implied in the show or by some other reputable source? Either way, I would say that so long as the color matches, it's not going to matter too much whether you make the sword out of acrylic or out of wood. Wood would be easiest. Slap on a bit of paint and voila. Maybe even have the paint glow a bit, since the sword seems to glow a bit in the show?
Another idea for the acrylic sword would be to frost it (or don't polish it after sanding) and stick some EL wire in it or some such, then hook that up to a battery, perhaps in the pommel? Then the sword would actually glow. The easiest way to accomplish that would be to make two halves of the sword, route out the grooves for the EL wire, then place the EL wire into the grooves, then use an acrylic solvent to "weld" the two pieces together. Bam, glowing sword!
Edit: Actually, the easiest way would be to simply cut out grooves in the finished sword and then stick the EL wire into that. That way you don't have to make two separate pieces and you could change it out if need be.