These look like they are available, at least here in the States, on Amazon here. Showing a few colors available between $21 to $34.

I do see there is some flexibility to that design with the magnetic closure.

Could one with a strap work for your application? The look of the case (minus the magnetic flap) immediately reminded me of the Quiver Pen Holder. If something like this would work, Quiver is just a brand name, a search for "pen case for notebook" on Amazon brings up many lower cost options.

Good Luck!