until you can get Amprol go to First State Vet supply online just google it. Please put powdered milk in their feed, it cant hurt and might just save the last one. I have been through this before, the powdered milk is not a cure but coats the intestines reducing the damage the cocci is causing. I would do it immediately and if it wont eat it try to force feed it a bit but you may loose this one too.
To be on the safe side first stop all antibiotic treatment since the cocci does not respond to it anyway and over medicating is just as bad as under.
Give powdered milk to all the chicks that you have now in their feed, even the ones that look fine, it cant hurt them and will only do good.
The get Amprol or corrid from somewhere. I highly recommend First state vet since he has smaller bottles than most people.
Treat all waterers in the coop those birds came from for a week to 10 days with the Amprol. Do the powdered milk in the feed as well. The Amprol blocks the vitamin B that the cocci needs to survive, it is much easier on the birds than any other Cocci remedy.
Soon your chicks will develop a resistance to the Cocci but some need help getting over the initial attack. Cocci is everywhere so it is unavoidable.
Good Luck.