I know the guys at work used to use the ceramic filaments from the burned out industrial lightbulbs to touch up their blades. It sounds savage but it worked
On a similar note, if you find broken ceramic dishes, any exposed smooth ceramic surfaces (often the bottom rim) work okay.
I have to second or third the use of diamond stones. They last functionally forever and are available in a wide assortment of grit. DMT makes a variety of different styles, ranging from large bench top stones to folding pocket sharpeners, many of them double sided so you have both a sharpening and honing surface in one tool.
If nothing else, just use a rock. Any hard, smooth, fine grained river stone will sharpen a knife acceptably for anybody but surgeons.
Sometimes it's easy to overthink this whole process of grinding metal. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />