BULLHEAD CITY, Ariz. — Carolyn Stewart had spent the past five months trying to find teachers for the Bullhead City School District, and now she walked into the Las Vegas airport holding up a sign with the name of her latest hire. The 75-year-old superintendent wandered through the international baggage claim, calling out a name she had just learned to pronounce. “Ms. Obreque?” she said. “Teacher Rose Jean Obreque?”