Taco Cabana just introduced "Brisket Tacos" and they taste JUST LIKE the shredded beef tacos I used to eat in California (except with soft flour tortillas, not hand fried corn tortillas, but still). So happy!
Now some other place (can't remember where...maybe "On the Border") also has something called "Brisket Tacos." They do have shredded beef, but it's marinaded in some sort of BBQ sauce that tastes very American, so I wasn't so thrilled with those.
If anyone else knows any places you can get shredded beef tacos in Texas, please share!