Ok, well, that's the keyboard one. That's pretty specific.
Although some would, I would never have an ereader without a front flap/cover. Even if it were just cloth on cardboard and a gaffer's tape hinge.
I've deconstructed the Poke5/Go6 cover and have a CAD (DXF) file of the front/back. It's 1 mm acrylic with cutouts for magnets. You could cover it with adhesive acrylic for a colorful cover. You can reuse the magnets in the stock cover or buy new ones if you don't have a cover. The plan was actually to make a transparent cover. People who like putting book covers as sleep screens might like that. The front magnets are not actually in the optimal place, but by a bit of rearranging you can make it so that all the magnets are on the bezel and not the screen. A bit of black spray paint on the magnets before laminating would make the cover less conspicuous. You could use colored translucent material too, either the acrylic or the laminate layer.
I used to have access to a laser cutter and it would have taken me less time to make this than a cup of coffee. Now I have to order it and have it shipped.