AMARILLO, Texas — The second-most abundant element in the universe is suddenly getting harder and harder to find. Party stores and florist shops grounded in the balloon business are caught in a helium shortage gripping suppliers across the country and in Texas, where one-third of the world's helium production is overseen. Supply of the noble gas — second only to hydrogen in the universe but rare on Earth in terms of quantity — has depleted while production from two large international sites is temporarily down. Not helping matters is scheduled maintenance at the U.S. Bureau of Land Management's National Helium...