There's some pictures on how to DIY. It's the plastic canvas you use in needlepoint easily bought at any craft store and the spines used for report covers you used to use in school.
I bought one of the ones from the store and didn't use their flimsy clear plastic, but the plastic mesh instead. It allows better water flow. I feel it is a lot more sturdy than my DIY one. My DIY one also has a piece of plexi glass with holes drilled in it because it was better support.
I wouldn't divide anything smaller than a 5 gallon though.