Ok, thank you everyone! I knew posting here would be the right thing to do! So many great answers.
You know, I am not all that sure that this feed store even sells Purina. I just got off the phone with another friend who told me about a couple of really great feed stores in the vicinity that I'll be checking out tomorrow on my Saturday ride (yes, I am also a scooter dork and I go riding on Saturdays LOL). I may not have much $$$ to spend right now, but at least I can find the places I'll need to go locally to BUY the right stuff. There's also a couple of feed stores in the phone book, and I'm gonna call around and ask if they carry what I want.
As far as the ages of my girls, the easter egger/ameraucana is, best as I can tell from pictures of other peoples' birds, about 12-14 weeks. She is the only one that is the actual age that I was told ALL my birds were, and she is much larger than everyone else ... that's why we call her Bertha. She's Big Bertha. LOL. She's bossy, too. We know who's in charge in the henhouse for sure. I think the other birds are maybe 10-11 weeks. When we got them, the leghorn was the smallest and had the smallest comb, but as time goes on, she's surpassing the others in comb development and has gotten "taller" and, like Bertha the easter-egger, is starting to sound more like a chicken and less like a bird. The rest all still make the "peep peep" sound, though it's getting deeper. They all have very small combs, mostly fleshy colored. RIR and welsummer had no combs at all when I brought them home. Barred rock's comb when I brought them home was barely visible but is becoming more prominent now. Easter egger doesn't appear to have a comb but has a "blank spot" between her eyes that is turning redder as time goes on and has maybe one or two "mini spikes" that could be considered comb-ish. I think that even though I was told the birds were "about 2-1/2, 3 months old" when I got them, I'm guessing they weren't even 2 months yet, based on what I've learned about their appearance as they mature since I've acquired them. Maybe you guys can tell from the description how old they are?? I'll see if I can get current pics of them to post, too.
Everyone seems healthy and happy. They get lots of clean air, love, attention, bugs, worms, fresh greens, and they're in a chicken ark and scratch the ground and eat bugs and grass all day. When we move the ark, I scatter a little grit and scratch grains at first until they tear up enough of the grass that I know they're eating more of the sandy dirt beneath.