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!

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.