My hens deal with 100 degree heat every summer and I havent lost one yet. I use a stand up mister that I got at Home Depot, it hooks to the hose. the hens do stand under it and it substantially cools down the air. Make sure they have plenty of shade, I freeze water bottles and put them in the waterer too and sometimes even lay them around the coop or run, usually the big gallon bottles. But really the mister is the main thing I do for them. At first they are scared of it but then once they get used to it, they love it.
On days I know are going to bereally hot, I spray down the whole run with water as then the hens burrow down in the wet soil later in the day to stay cooler.
Sorry about your hens! Hope your others survive the heat spell!
Nancy