If you can't get these, fill empty plastic bottles 3/4's of the way allowing room for expansion. Every bunny will appreciate them whether 2 ltr or 20 oz size. I carry them from freezer to rabbitry in the cloth shopping bags or a bucket.
Other ways to keep the bunnies cool is to wet their ears with cool water, take care not to get water down inside the ears. Just dip your hand and wipe over their ears.
Some will wet and freeze a towel for bunny to lay on. Just make sure to remove when the coolness is gone. Removing when it is no longer helpful, allows the air circulation to continue. Some folks wet towels and put over the tops of the cages.
When we had the old rabbitry with a white fiberglass roof, we would spray a hose back and forth on the roof and after just 5 minutes, it cooled the inside TEN degrees!!! Some folks will put a soaker hose on their roof.
If you see a bunny in distress, put it in a carrier and bring into the house til evening when it cools off. Pregnant and nursing does are especially susceptible. Keep an eye on them. A warm bunny will pant some. If you see a rabbit panting AND it is wet around the mouth and nose, it is in trouble. They can withstand cold easier than heat. Their only source of releasing heat is thru their ears. Some larger breeds have trouble because of their body size. They have larger ears but bigger body mass.
Make sure you have good ventilation and air moving. Even when a fan is blowing warm air around, the point is that it is moving air and creating air exchanges. That is important for odor control also.
Now is the time to use those fans. I bet the electric meter is just a-hummin' while we have 5 fans running, some oscillating to move air around as much as to cool the air. The rabbitry has good insulation in the roof and a concrete floor that helps keep the building cooler. Course in this weather ihe floor sweats, so we have to be careful not to slip.
Make sure they always, always have fresh clean water. The rabbits won't each much during the hot days but will eat more at night.
Was happy to hear that a doe I'd sold last month waited until the early cooler hours to deliver a litter of 8!!!