Over here in Thailand, the birds are born mostly on farms and sold by the farm or a middleman. They do not want to feed a bird or usually, you will not find anyone selling them after 12 weeks. All the birds I purchase has been between 4 and 5 weeks old. I have hand feed all 6 of our birds until they wean.
I live in Thailand and here most vets only handle Dogs and Cats and have no or very little knowledge of birds. The nearest Avian vets. is around 60 miles from my home. It is located at a University Animal Hospital. Of course, I would take our birds there when required but we do want to make sure we have a good reason for doing it. My daughter is a Vet in America but doesn't really works with birds but she has some knowledge and it helps. Just need to keep them healthy so they don't have to go often.