An MSN search (I wasn't curious enough to Google) turns up:

SoCal Society for Ethnomusicology has a "members list" link. You might find someone (or a few) you know who could give more direct advice.

SEM Homepage has a "contact the society" link with email clickies to the President and to the Society Office. It's possible they have information on "accredited" courses.

UCLA Department, since it seems in your neighborhood, includes their course requirements if you follow the links. It doesn't appear that they have a web-based program, and the inclusion of "performance" sessions as a requirement would seem to mandate on-site presence. (They also seem to disparage MA candidates who don't intend to seek the Ph.D.)

There seem to be only about a half-dozen schools offering this course of study (in the US & Canada), and their requirements look pretty similar. I'd be dubious that the requirements they list could be met through web study, but it's certainly worth looking further before reaching any conclusions.

John