First off, take a look at this and see if it will do what you are looking for. Blender can export to DXF and if this program will import it and convert it, problem solved! The manual should give you a good idea of the capabilities.
If not, here is a script already written, it may do what you want:
http://blenderartists.org/forum/showthread.php?t=44018
If neither of those are what you’re looking for, go ahead an describe the project. There appear to be many different “standards” for cnc notation, so It’s going to be of questionable usefulness to write an exporter for a single format. On the other hand, I suspect most cnc machines will import g-code, so it could be quite useful.