Do you mean buying day-old chicks and putting them with the hens? If so, then you might be able to do that, but many things would have to line up just right for you. First, the hens will have to go broody. This is a hormonal change, and you can't make it happen. Watch for them to not want to leave the nest, growl at you when you try to take them out, and still be in that same nest when you come back to look that evening. If you get one that's broody, put her in a secluded place such as a dog crate where the other hen can't get to her with a nest and some fake eggs. Golf balls are fine. Hens aren't smart. Close her into the new nest. Watch her for two days to see if she's going to sit on the eggs or if she's too unhappy with being moved. If she sits, let her sit on the fake eggs for a few days. One night, remove the eggs and tuck the day-old chicks under her. This might work. Be prepared with a nice warm brooder just in case she rejects the babies.
As you can see, this is a tricky business. Good luck!
That didn't work for my hen, she looked at those babies as if to say where the H did you come from? So I had to take them out, she wanted Nothing to do with them. So I went on ebay and ordered her fertilized eggs, gave them to her , she hatched them and loved her babies ! I've done that three times with her and it worked great every time.