You can do it using Python:
>>> import os
... workspace = r'C:\junk'
... lyr_dict = {}
... for root, dirs, files in os.walk(workspace, topdown=True):
... for file in files:
... if file.endswith('.mxd'):
... mxd = arcpy.mapping.MapDocument(os.path.join(root,file))
... lyrs = arcpy.mapping.ListLayers(mxd)
... for lyr in lyrs:
... if lyr.supports('dataSource'):
... lyr_dict.setdefault(lyr.dataSource,[]).append(mxd.filePath)
The above script creates a dictionary like {layer_path1:[mxd,mxd,mxd...], layer_path2:[mxd,mxd,mxd...]...}