I live in central Texas. I have 3 suggestions.
#1 - cheap & easy - hang some towels, burlap sacks, etc either inside, or on top of the cages so they get wet from the mister. You're basically making an evaporative cooler. When I did this, I did not use a fan because it replaced the cooler air with hot air.
#2 - put shade cloth OVER the top of the metal roof. Try to keep it off the roof by a few inches. PVC pipes, ropes etc can be put under it to lift it. You'd be amazed how much difference it can make.
Put your hand up to the ceiling without the cloth - if it's like mine, it will feel like a broiler radiating heat into the rabbit cages.
#3 - possible? I was able to make a (much) smaller pen that would hold the cages and I moved them to a tree-filled area. It is routinely 10 degrees cooler than the rest of the yard. If that's a possibility, you might want to try that. I have to have mine within a larger pen because there are feral dogs and coyotes that would love a nice fat rabbit. (or 10)
Good luck! - Liz