I agree with this ^^I also think it is important to know what was killing your own birds before you bring in any new ones, otherwise you may just continue to have more losses.
Stress increases the chances of disease breaking out and spreading. Integration of new birds causes stress.
@HuskerHens18
How many chickens do you currently have? How many Hens and roosters? What are there ages?
Do you have other fowl - turkeys or ducks?
Photos of your current flock, housing and run(s) would be helpful.
I can't find any place where you posted the official results of the testing/necropsy - can you give us more information as to what the reports stated?
Please do not take this the wrong way - I took a very quick look at your previous posts, especially the one's in the ER threads, it looks like you have been dealing with a multitude of things - Coccidiosis, some type of respiratory illness and/or possibly bacterial infection (speculation on my part by looking at some of the poop you posted).
I understand that you have had testing/necropsy and spend $$$ trying to figure all this out. I can't imagine losing that many birds in such a short period of time and it must be heartbreaking.
I would not only be concerned that started pullets may bring in another unknown illness/condition, but unless you get a handle on what caused the death of so many chickens, I would also be concerned that the new birds may pick up something from your current flock. This may result in more deaths and heartbreak.
There is not a really "good answer" in this particular situation. You can try it and see how it goes.
If you do get the pullets, then quarantine is a good idea. I would definitely either feed medicated chick starter or have Corid on hand, you could always give a preventative dosage of Corid if you don't use medicated feed.