Stanford source aggregates the available online copies of various Machaut MSS.
HOLDING MESSAGE: While the Stanford site is down, the following links go to the relevant pages on Gallica for the main Machaut sources:
Manuscript Studies in an Interoperable Environment doesn’t sound like the most enticing site ever titled, but this project, based at Stanford University, really should get the pulse of any Machaut scholar racing. One of its pages aggregates and provides links to the various Machaut MSS currently online. My future Machaut classes are going to be so much more visually attractive than they were in the days of my reliance on black-and-white photocopies from microfilm!