You're right - I don't see anything out there except corn flake boxes. But don't sell yourself short - you could probably pick up the ability to model a corn flake with about an hour's worth of tutorials on polygonal modeling.
Put a cornflake on your table as a reference, get the profile right, make a couple of noise modifiers to make the roughness and bowl shape (of the flake), then add a Cellular bump map, and you're good to go.
I agree with Joe. If you play with a cellular or noise filter in the displacement channel of your material, it might be easy to turn a circle (with slight extrusion) into a custom cornflake. Sometimes the displacement modifier, applied to the object, works better than adding the map directly to the material. You may want the material to be somewhat translucent, as some light should pass through a cornflake.
You should even be able to build one flake, and then instance it, via PFlow, to create a pouring stream of flakes.
It really is that simple. And you'll take your first step into the world of poly modeling. The real trick to it is using good reference material. I did a Google search on "corn flake", and set it to "images", and was suddenly looking at hundreds of reference images of corn flakes, by the bowl, by the box, by themselves...