These new Digimon will only be available for Capsule Digi-egg evolution from now until September 11th. Until September 23rd, there will also be an event running where players can gain items simply by staying logged on to the game.
This includes coins which can be exchanged for a variety of items. 25 coins nets you a Digi-egg of Miracle, which will let you hatch a Magnamon with 100% success rate. You can find more details here.
Digimon Masters is out now on PC.