General Motors Co. ordered a half-million replacement ignition switches to fix Chevrolet Cobalts and other small cars almost two months before it alerted federal safety regulators to the problem, according to emails viewed by The Wall Street Journal.

The parts order, not publicly disclosed by GM, and its timing are sure to give fodder to lawyers suing GM and looking to poke holes in a timetable the auto maker gave for its recall of 2.5 million vehicles. The recall concerns a switch issue that is now linked to 30 deaths and...