Most wild-caught bettas I have seen in pictures look skinny. I think they are usually pretty skinny and beat up when they get pulled out of the wild. Some of my wilds were pitifully tiny when I got them and now they are much bigger.
Most of these fish are endangered because of habitat destruction rather than overfishing so it is good to have them in the hands of hobbyists to keep their numbers secure.
Also many species can be found as captive bred stock. You just have to know where to look (I am not sure where that would be in America sorry).
Also because this is the picture thread. Here is the same male flaring.