I bought mine from Rockler. It is handy for when you have a half sheet sander or a quarter sheet sander,, which I don't use those much at all any more. But I still buy sheet sand paper for doing some hand sanding every now and then. Never have to use the hack saw blade, or scissors, or a knife or the fold and fold and fold and tear method.
https://www.rockler.com/rockler-sandpaper-cutter