Feeling your pain, here in the Hill Country. If you have a sandy or dirt area in the shade (or create one), keep it wet it down so chooks can lay down in it. I also have a very shallow, large diameter tray (like sits under a potted plant) that gets replenished daily with cool water. Some girls stand in it, others just drink from it.
My girls free range during the day but sleep/lay in their coop. Re-freezable ice packs alongside the nest boxes, plus on the poop boards (just behind the roosts) in the coop each night. Makes me feel better, not sure if it helps. Plus an outdoor-rated fan with covered motor, running nearly 24 hrs a day/night pushing air through their coop.
Temps yesterday hit 100F inside the barn, 102F on the back porch--first time ever. Got a reprieve this morning with....69F to start the day but already heating up. Hang in there.