Quarantine is important if you have a very valuable flock, either due to numbers or quality breeding program. Or if you would be at an emotional loss to lose one of your birds. Frankly you are only risking one bird.
I would try and get birds locally, and you might get them. Contact your feed store, the county extension agent, or a poultry club to find other crazy chicken people. Someone will know someone that might have what you are looking for.
I too, echo bobbi-jo, do not get birds from a flea market or auction. I belong to another group, and they make my blood run cold how they add birds willy nilly.
If you get them quickly, and add them at night, you really might not have much integration problems. Do make sure you have some hideouts set up in your set up.
Mrs K