@lindachick ! I'm sorry about your losses! Where'd you get your three new chickens? You'd better get some company for your lone Americauna. If you got them from a hatchery you probably don't need to quarantine.
Honestly, unless you have the ability to properly quarantine, I wouldn't bother because you're really not doing any good anyway. I don't often bring in new birds, but when I do it's from known sources. A friend with a healthy flock or a hatchery. I would not buy them from a flea market or animal swap because I don't know where they've come from or what kind of conditions they've been under.
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.