To the best of my knowledge, tetron is polyester. It's a trade name used by Teijin, I believe. Polyester has been marketed under the names of terylon, dacron, etc...
Although I wear polyester hakama (check out the ones from Iwata), I have to admit that you can't duplicate the look of indigo-dyed cotton.
If you take a look at the Mugendo Budogu site, you will notice a top grade indigo-dyed cotton hakama that has been treated in such a way as to be colorfast:
For the indigo dye to be color fast, typically you will need a "fixing agent" of some kind; some fixing agents are supposed to work because they form a thin film on the fabric, thus improving rubfastness. I figure this would be about the only way to improve indigo's rubfastness. In most cases, this will change the handle, or feel, of the fabric. Just wondering if someone has one of these, or whether the esteemed Budo Bum can tell us more about these hakama.