Well, some days before I decided to use US, I was choosing Singapore as my region so I've locked with Forest Vivi on the day I started it on the first time. And it was before I discovered that I can't buy eShop games when I set it to Singapore.
So you ended up choosing someplace in the US as your "region". What Vivillon form did you end up with btw? I'm thinking it might be something like Modern, Polar or High Plains since those three dominate the US.