You can make your own cool mat. Even an old pillowcase will do. Sew lengthwise 1.5" channels, add 2 tsp Soil Moist (polimer granules, available at Agway) and stirch end together.
The more cotton like and porous the fabric the better. These take a l-o-n-g time to dry, and therefore can mildew. "Plump" up your mat by soaking in cold water and place somewhere convenient for your dog to lay. I found using the resin tray from the dog crate works great to place the cool mat.
www.ceannmor.com/cool_ties_cool_mats.htm