I can’t even fathom what 108 feels like but I can feel your chickens’ pain. Yesterday, we hit 95 and my Easter Egger was panting like a dog. We’re expecting 98 tomorrow.
I second the bricks in a pan of cool water. Not all chickens will want to stand on them but I made my chickens stand on them yesterday anyway to cool them down. Also I second the fans in the run. They hang out in front of them all day. I place one blowing into the big butterfly bush in their run and they love it there as they bury themselves in the cool earth. I also put tarps and shade cloth over the run to create more deep shade, pour water in the shady area to cool the ground and crank up the fans to high. I move a fan into the coop at night and add frozen water bottles in there. Electrolytes in the water too and then add ice throughout the day. Cold plain yogurt is a favorite of theirs for hot days.
I plan to bathe my Easter Egger today to cool her and to clean her poopy butt. She always suffers more in the heat even compared to my heavy dual purpose birds. Any chicken that seems to be suffering will get the same treatment.