Three patterns are available: Meadow, Marine, and Garden. Meadow Pattern is the default form found throughout the main game, of course. Garden Vivillon are found in the Mega Dimension DLC.
As you'd expect, the game already has data and Pokédex entries for the remaining forms, which can be seen by hacking them in:
And to clarify, the Spewpa you get from the Lumiose Museum is the only way to obtain the Marine Pattern right now.
Home support is expected to be added sometime later this year, so it will be possible to transfer the rest over at some point.
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