I got some BT 70 (approx.) sized stuff at a Las Vegas launch years ago. It's fiberglass over phenolic and was ment for high voltage conduit. I contacted the maker, they asked me where I got it and did tell me that it's avalable in 1.5" (or so) up to 6".
It's been so long ago I can't remember the source I guess you could try a search yourself.
Hawk Mountain has fiberglass airframe tubing down to 1.145" ID. For light tubing, the best I've been laminating a wrap of 2oz cloth onto a cardboard tube.
My latest technique is this. Working with BT80, I slip coupler tubes inside to stiffen it while working. You can wrap the end ones with plastic wrap from the kitchen to keep from epoxying them in place accidentally. Then, I use a foam trim roller to apply laminating epoxy to the tube. Cut the glass about 1/2" wider than it needs to be to allow some overlap. Cutting it on a 45 degree angle will keep the edges from fraying, but you have to be careful handling it once cut because pulling on the ends will make it shrink in width. Drape the glass across the tubing and use the roller to work it around and get the wrinkles out. You don't want to have epoxy drooling off, just enough to wet the cloth out so it is transparent. Now, cut a piece of low temperature plastic covering material from your local hobby shop (Nonokote, etc.) to the same size as the glass cloth, about 1/2" oversize, and start wrapping it around the glassed tube, working out wrinkles as you go. Iron the edge closed. Now use a heat gun to shrink the tube, working from the middle to the ends so no air is trapped. If you get bubbles, puncture them with a pin or hobby knife to let the air out. You can also wrap a cloth around the tube and force the air to the ends. You need the cloth because the covering will be hot. The result is a pre-finished tube. You can't surface mount the fins on this, but with through-the-wall construction, you can apply fillets on the inside and it is smooth and strong. We core-sampled a muddy field with some LOC 2.56" tubing treated this way last Saturday and flew again after pulling out the 5" of mud and cutting off about 1/2" of frayed tubing.