import arcpy.mapping as mapping, os
path = r"C:"
f = open('BrokenDataList.txt','w')
for root,dirs,files in os.walk(path):
	for filename in files:
		basename, extension = os.path.splitext(filename)
		if extension == ".mxd":
			fullPath = os.path.join(path,filename)
			mxd = mapping.MapDocument(fullPath)
			f.write("MXD: " + filename + "\n")
			brknList = mapping.ListBrokenDataSources(mxd)
			for brknItem in brknList:
				f.write("\t" + brknItem.name + "\n")
f.close()
