I got mine from a big box pet store. I definitely would have preferred getting from an ethical breeder, but I had no way of knowing which were and which weren't last summer when I got him. There were some breeders on craigslist but even their pictures seemed sketchy so I just didn't know how to find a good one. I don't know anyone with a parakeet so had no one to ask.
When I finally decided to go to the box store I realized, you know what? These guys also may have come from a bad breeder and who knows what bad things the store may have done to him....so I kind of looked at him like a rescue. He is already alive and needs a good life and regardless that the big store will get my money, this little guy still needs a good home. At least at the store I could see his environment that he had been in and was reasonably assured that he probably wasn't sick (or their whole flock would be sick). Got him home, definitely not sick just very skittish (at first).
Of course I only have the 1 bird so it is different if buying a possibly sick pet store bird and bringing him/her into your home with another bird. Mine was a baby and had no signs of problems with his feathers, etc. and no other birds already at my place, so it was a safe risk I think.
If I were to get a second bird, I would go back to craiglist and look into the ones that are being rehomed. There is always someone who got the bird and didn't realize how much time they actually require and then they re-home them. And if there weren't any available like that on one particular day, just wait a few days or a week and one always turns up.