I'm in the same situation that you are. I purchased an SWEP1 two years ago at an auction that had been stripped for parts. All of the toys were gone including the lightsaber assembly. I've been able to find all of the parts for the lightsaber now except the green plastic tube. This week I stumbled across fluorescent tube guards and I'm thinking that they may work. I have the plastic tie downs for the tube and it looks like the tube should be about an inch in outside diamater. That would make the T8 tube guard about the right size (The clear T8 tube guard that I measured in Home Depot was 1 1/4" OD). I wish I had a real tube to measure so that I could be sure. But these look like possible options:
They have blue and red options as well if you prefer. Just to re-iterate, I haven't tried this yet. I don't know if they are the right size or thickness. They are just the closest thing that I have found so far.