Depending on how old your birds are, a proper chicken feed will look similar to Cream of Wheat or to rabbit food. If that seed is all you have to feed your (older) birds, it'll do them for a day or two until you can find real chicken food. But it's not going to be good to feed them that long-term. Depending on age, you can feed your chickens: bread, yogurt, oatmeal, leftover/wilting veggies, rice, beans, spaghetti, scrambled eggs, hamburger... just about anything you would eat! But this should not be all they eat. They need a balanced diet, and for that the best ways are actual chicken feed plus free-ranging if possible.
Pet stores are probably not going to have ANY chicken supplies. I think only one nearby me does, and even that is very, very limited. It's just easier to go to the feed store.