In California, you can go to places like the Rose bowl flea market. And besides home/entertainment antiques, they also have a gigantic clothes section. It seriously is endless. Im pretty sure many vintage retailers come here to either trade or buy the clothes they sell to other people, because they can find such great deals. But it's also open to the public, so I've been able to find so many great things there. A store by where I live admitted they get some stuff from Japan, go figure. I wonder when all the vintage resources will finally be tapped.
My mother still had, luckily, a lot of her vintage clothes from her youth in Mexico. I asked her what happened to a lot of that clothes now. She said that people never had a penchant for old clothes where she lived. And that if it has been kept, it's in some sort of dark storage in personal homes. Supposedly her dad made a makeshift mattress full of their vintage clothes - the mattress may be elusive and gone...but I wonder if it really exists. Now that would be strange.