So far mine are doing pretty well with no misters. The 2 production reds and a hatchery barred rock, all about 2 years old, are panting some during the hottest part of the day, but don't seem to be too stressed about it. They're still laying. My coop is open on one side with hardware cloth-covered windows in two of the three other sides. The attached, hardware cloth-enclosed run has a bunch of 70% shadecloth strung up on the west side. The chickens have a black rubber dog bowl of water to stand in if they want. Usually they just stand on the edge and poop into it. Then drink it.
I put a second "roof" of shadecloth over the metal coop/run roof a few weeks ago, and that is helping keep the temps down a lot. The shadecloth "roof" consists of a wood frame, with the shadecloth supported by wire re-mesh panels that are attached to the frame. The shadecloth is stapled to the wood, and additional wood furring strips are screwed down on top to help hold the shadecloth in place. The whole contraption was built on the ground, then lifted on top of the coop and tied down with simpson straps. Looks kinda crazy, but it's doing a good job keeping things cooler! My yard is one of those scorched-earth desert lots that some former owner scraped down to nothing. Only have a couple of trees and none of 'em was anywhere near where we could put the coop. I can't get weeds to grow in most places here, let alone trees. Hence the shadecloth.

I put a second "roof" of shadecloth over the metal coop/run roof a few weeks ago, and that is helping keep the temps down a lot. The shadecloth "roof" consists of a wood frame, with the shadecloth supported by wire re-mesh panels that are attached to the frame. The shadecloth is stapled to the wood, and additional wood furring strips are screwed down on top to help hold the shadecloth in place. The whole contraption was built on the ground, then lifted on top of the coop and tied down with simpson straps. Looks kinda crazy, but it's doing a good job keeping things cooler! My yard is one of those scorched-earth desert lots that some former owner scraped down to nothing. Only have a couple of trees and none of 'em was anywhere near where we could put the coop. I can't get weeds to grow in most places here, let alone trees. Hence the shadecloth.