Back when I picked up a SWE1, I needed a new light saber and went with this:

http://www.woofersetc.com/p-1736-g24s-toxic-green-24-straight-neon-light-bar.aspx

After receiving it, it does work great but there are a few differences. The tube is clear rather than green. Actually the bulb is white until it turns on, then it is green. It is a bit shorter, so I had to move it up further in the saber handle (and it still is a little short, but not bad), which is not the greatest fit. It seems to have a little smaller diameter. I'm sure the overall coloring effect is a bit different, but since it wasn't working when I got the machine, I cannot personally tell (YMMV).

Also, the transformer is built into it, so all you need is this part (and the saber handle if you do not have it). I've been very happy with it.

There was one in the link that SealClubber provided. Beyond that, I have not seen these tubes for sale anywhere else.

Update: That site does not allow you to put one in your cart - so apparently they are out of stock on them.