Obvs the Pinball Hall of Fame in Las Vegas. Easy to get to and Vegas is a blast in addition to pinball, even if you don't gamble.
Other ideas ... Allentown show in the spring. There's an airport right there, or it's close to Philadelphia. Maybe American Pinball in Chicago offers factory tours? Sunshine Laundromat in NYC? You should definitely visit New York if you've never been, and Chicago and Philly are great too.