Welcome! Not sure if you read this, but in the summer I take those little drinking bottles and 2 liter coke bottles, add water and freeze. Then just rotate them in and out of the coop. I am on a rain water system so I can't do a mister, but this just reuses the same water over and over again. they get a little dirty so I throw them in a plastic bag before I put them in the freezer. the chickens love them and fight over who gets to stand on them, very funny to watch
Also, I bought some of that "shade screen" from Home Depot and just throw it over the coop in the summer and then take it down for the winter, it really does keep it 10-15 degrees cooler.