Google "plastics" near your area if you haven't already done so
The closest place to me is S&W plastics
They carry smaller/thinner sheets of acrylic and all the weld on stuff to connect it, they might even cut to order. Most of the stuff would be big and thick enough for small to medium overflows and smaller diy projects. They might be able to order bigger stuff though of your trying to build a tank or something
5158 Holt Blvd., Montclair, CA 91763 Phone: (909) 621-4887
Sandwplastics.com
Hope this helps