A company called "Duosharp" makes plastic mounted diamond plates (the plastic has diamonds embedded in it) doesn't look like much, and it's price seems excessive at about $100.00 for a bit of plastic plus the base to use it for chisels is extra.
However, the plate is thin enough to fit inside the cutout in most router bits (don't try to grind the outer edge, you'll change the diameter and destroy the usefulness of something like a lock miter bit) but a few strokes on each face (same number each side) will bring it back to performing like new. (use water for cooling and lube on the plate,dry off and wipe off and then spray the bit with oil or bit lube afterwards).
I maintain literally hundreds of router bits this way, some small bits won't fit but those are cheap and disposable anyway. A good bit will stand many sharpenings before needing to be replaced. get a good magnifying lens to check for sharpness and to check for divots (chips in the edge).
