According to Serebii, a Pokemon news site said that a new Dynamax Crystal event is making its way to Pokemon Sword and Shield. In this event, it stated that you would need to get a code from specific video game retailers, and that code will grant you a Dynamax Crystal. The crystal can be used to activate the Gigantamax Copperajah Max Raid Battle located in the Watchtower Ruins.
It appears that only GameMania in Netherlands and Gamespot in Germany has rolled out this event, but I’m sure more regions will see this soon. The Dynamax Crystal event for Gigantamax Copperajah will go on from June 5 to July 5, 2020.