"If a company was found guilty of antitrust violation in a state court, it would have to obey the judgment, even if it had been found not guilty in other states. So, the Buck-Lee bill could result in a single state judge overriding the decisions of all other state and federal judges."

This is true, but is already the case under the existing "separate sovereign doctrine" which holds (generally) that prosecutions in different states (or in state and federal courts) do not run afoul of the Constitution's double jeopardy clause.