Reuters) - At least 122 firearms from a botched U.S. undercover operation have been found at crime scenes in Mexico or intercepted en route to drug cartels there, Mexican authorities found AK-47 assault rifles, powerful .50 caliber rifles and other weapons in late 2009 that were later linked to the U.S. sting operation to trace weapons going across the border to Mexico, Guns from the program, dubbed "Operation Fast and Furious," also were found at the scene of the murder of a U.S. Border Patrol agent in the border state Arizona last December. It is not clear if they were...