Are they in a cage or a tank? You can put a fan in but don't aim it directly on them because fans tend to get all the nasty stuff from the air and just blow it all over the place. Put a bowl of ice in front of a fan and it'll make instant AC.
You can give them frozen watery foods like watermelon and grapes. Also you can freeze water bottles, wrap them in a towel or a sock and just stick it in the cage...I would watch and make sure they don't chew on it though.
They make chinchilla stone things that you put in the freezer and they stay cool for a long time. You can also go to a hardware store and just get a piece of marble time and stick that in the freezer