By Timothy Aeppel (Reuters) – John Ehresmann loves that the cost of shipping an ocean container from Asia to a U.S. port or buying a load of lumber has fallen back to earth. If only that were true for everything he buys – but it’s not. Some parts of his supply chain have clearly improved, said the vice president of global supply for Graco Inc, the Minneapolis-based maker of fluid handling equipment such as paint sprayers. But the complex nature of global supply chains means that companies like Graco are still struggling, since the shortage of just one part can hobble them. “Not having that one…