When Jose Camarena moved to Texas in 1981 with his wife Sylvia, he had a mission in mind. He wanted to buy a taco truck and sell his food on the street corners of Houston, much as he had done in Chicago for the previous two years. Mr. Camarena was startled to discover that Houston had few, if any, of the taquerias that were so popular in Mexico and Chicago. There were plenty of Mexican restaurants here, but not the tiny businesses that sell tacos fast and cheap, authentic Mexican style.