You can get high-temperature appliance touch-up paint from nearly every large store (department store, home improvement center, hardware store, appliance parts stores, etc.).
The area needs to be sanded shiny then cleaned with alcohol, acetone, minerals spirits, or another fast-drying cleanner or solvent before applying the touch-up spray.
If the paint is allowed to dry according to the instructions, it shoudl actually last for years.
It's important to wipe up moisture and spills when they occur, too.
William E Miller † MicrowaveDisplay.com, March 2007