The other night at the Iain McCaig lecture, I (Scott) saw Vic Mignogna from Lightsaber World approach Iain with a question. He wanted to know what kind of fabric Obi-Wan's costume was made from. Vic had been searching for an identical match, but had no luck. Vic lets us know what Iain told him:

All the Jedi Costumes were made out of a material called Indian Homespun. It is a light woven fabric like Ghandi wore. It is hand woven in a variety of different patterns and shade of white to tan. That is why so many Jedi tunics were different shades. They also dyed the same fabric black for the Sith robes.

You can find this fabric at some Indian stores. Hopefully you can find an exact match! Thanks to Vic for the report!