You do not need Cell cast acrylic, Many years ago cast acrylic was held to tighter tolerances than extruded acrylic... It also had fewer flaws. In the last 10 years huge strides have been made in extruded acrylic. The only downfall is extruded acrylic is only seen it available in thicknesses up to 3/4 or so. I have been building with acrylic for over 15yrs in my sign shop, I have made many tanks with both cast and extruded. If you are still set on cast acrylic you are going to pay more for it. Wensco sign supply sells cast acrylic in 100" sheets and many thicknesses.. Any sign shop in your area should be able to get it for you. 51x100 sheet of 1/2" cost me about $255. 3/8" cost about 190 a 51x100 sheet. If you can't find someone that will order it for you let me know and I can arrange it for you.