Check out the mics at
www.thesoundprofessionals.com
They have a wide variety of just about any type of mic you could want- including many that are specific to MD and DAT recording (and on many different budgets). I personally use one of their Audio-Technica mini binaural sets for my Sony RH-10. They also have preamps neccesary for recording in high SPL situations (which you plug into the "line-in" rather than "mic in" on your MD recorder). I personally am not too fond of most of the Sony mics, as many are built with a certain degree of bass-rolloff, meant to stop from overloading the pre on MD recorders (which are sensitive to bass frequencies).
Karl