you could get/save some plastic bottles (like 2 liter soda bottles) & fill them almost full with water & freeze them. Leave room for expansion in the bottle. On days like this, take a bottle out of the freezer & put it in with your rabbit(s).
We have meat rabbits, they get frozen bottles and do fine. They have shade, fresh, cool water from a water system and their frozen bottles. They do fine. I've seen our evil inside rabbit acting like he's hotter in the A/C than the outside crew.
DONOT WET YOUR RABBITS! especielly in hot weather you can cause them to go into shock and die. you could rub there ears with a warm(cold water could also cause shock or atleast discomfort) damp cloth that would be ok but no matter how hot a wild rabbit gets it will NEVER EVER submerse itself in water.
I would surely wet down any rabbit without hesitation that is heat stressed, wetting them down as often as needed (2-3x daily as needed) if the temps are high and the air around them is not cooled with misters and fans. And also thoroughly wet down the ground around their pens if they have reflective heat. Once heat stressed, just giving them ice bottles will not cool them down fast enough.
My rabbits love to be thoroughly and gently wet down in hot weather and it gives them refreshing relief instantly that will last for about 3 hours. No water inside the ears or nose, of course.
Rabbits will often lay at least part way in their water crocks in hot weather.
Wetting down healthy rabbits with tepid water will not harm them at all in hot weather. They dry quickly. Mine that are outside line up next to their doors for their turn of a cooling, wet massage when they see me coming with the water jugs. I put one hand over their eyes/nose while at the same time blocking water from going into the ears, and slowly pour water over them, massaging it down to the skin. Please note I have NZ & Cals. But any breed with heat stress will be cooled quickly by wetting them down, coat be darned (a nice coat won't matter much on a dead rabbit
Keeping a spray mister along for human use when wetting them down will help keep their humans cooled off during the process.