Can you be specific of which Moga you are referring to? There are so many Mogas, it's hard to figure out which one you've meant.
If you're talking about the Gryph, you need to contact the developers. Bottom left side of their account.
If you're talking about the Icevia, I apologize but it's an one-day only gift. However, you can find it in the wild. The problem is Icevia is hard to find and no one knows where Icevia is located.
If you're talking about the latest Mogas, you have to get Moga Cards to trade the seven new Mogas. The others are not released in the game. To get Moga Cards, you have to battle the Mogas. To find which Moga Cards you need, click the Collection button next to the Quest button.