Folks in the industry bought licenses, tooling, and parts for games from manufacturers that shut down. Others were reverse-engineered after the fact. Between https://www.pbresource.com, https://www.pinballlife.com, https://www.marcospecialties.com, https://www.actionpinball.com, and https://www.planetarypinball.com you can find parts for many machines going all the way back to the 50s.