Here's what we have done for the extreme heat in Texas and it works very well...
I was loosing chickens also last year due to the heat since some days it got up to 110 degrees. We went to Lowe's and bought some of the misters that people use on decks and you sometimes see them at restaurants that have eating outside. You can buy the kits for about $25.00 or you can buy some PVC pipe and just purchase the misters separate, which is what we did. We ran a row of PVC pipe over their run far enough away from their food so that it wouldn't get damp. We drilled holes in the PVC pipe big enough to insert the little misters and then put an end cap on one end and threaded a PVC joint that will allow you to hook up your garden hose to it (the sales representative can help you there). Then we just turned on the water hose (VERY VERY LOW). Just enough pressure to give you a mist coming out. It will drop the temperature in the run by 10 degrees definitely! My chickens at first were scared of it, but I just left it on and when they got use to it, they eventually went and laid down under the mist during the hottest part of the day.
I have also put water in those little plastic kiddie pools and put ice cubes in it. Some chickens will get in it and other won't. If you start them out with it at a young age and they start to drink out of it....they will eventually get in it.
I have also frozen 2 liter bottles in the freezer and put that in their 10 gallon waterers to help cool the water.
Also, if you'll get some sand and put in the run and keep that wet....they will lay down in it too!
Hope those ideas help. The misters are what worked the best for us and didn't cost a fortune in the water bill!