Tube
I know I have.
Because of this, I have decided to turn my scientific PhD talents (I got my certificate off the same site Gillian McKieth did, so there) to solving this problem. At first I tried simply creating yet another bloody Sudoku book, but that didn't work since the market is already saturated with the freaking things as it is. I then experimented with a form of mail-order : when a Sudoku is required, a small charter plane will fly overhead and drop a crate containing a single Suduko at your location. This was deemed unsustainable in the long run. My third attempt saw somekind of high-speed Sudoku tube network all across the world, but a papercut decaptiation brought this to an end. (A side note to my lawyers : What am I paying you for, you useless shits? GET ME OUT OF JAIL YOU ASSHOLES.)
Back to the topic at hand, I have created the most remarkable thing since Daikatana was ported to yet another console - Sudoku in a Tube!
Patent Description : The product is a tube, roughly cylindrical with little squashed bits at each end (on a side note, I name this shape a "Squashed-Sasquatch-Matrix-Tube"). The tube is filled with nothing but quantum sudoku, distilled from the finest papermills in Japan. When squeezed, a material approximately the consistency of toothpaste will emerge with a partially completed Sudoku. Spread over a wide enough area and the entire puzzle will become visible, and the product will instantly harden to allow drawing on it. Pens are not provided.
It contains around 200 sudokus of varying difficulty. At this moment I have not figured out a way to regulate the difficulty, so simple-minded individuals might become momentarily flabbergasted. But panic not - simply squeeze out another irremovable Sudoku on a wall or bus-stop, and voila! Another Sudoku.
NOTE : Negative effects occur when sprayed directly on human face. These effects may include suffocation.
Evaluation : Comprehensive testing from the Patent Standards committee has shown this to be "irredeemably dumb and of no value whatsoever". Comparisons were drawn to other products with a similar evaluation, namely the Phantom.