Hello,
You can read the mxd or mapx file in the service's directory with arcpy in Python too. You will find database / file source and the layer's ID with which you can make the connection between database and service.
You can find the path to the mxd file in the service properties. Do a loop on all services to have all files of all services.
Managing GIS Servers with Python 
Work with arcpy and ArcGIS Project 
# Create temporary ArcGIS Projec to import service file
aprx = arcpy.mp.ArcGISProject(r"C:\projectArcGISPRO.aprx")
# Import service file with file path in service's properties
aprx.importDocument(filepath)
#List all maps in ArcGIS PRO
mapList = aprx.listMaps()
    for m in mapList:
        #List layers in map
        layerList = m.listLayers()
        for l in layerList:
            if not l.isGroupLayer:
                if l.supports("DATASOURCE"):
                    #Find datasource 
                    datasource = l.dataSource
                    #Find layerID used in service
                    layerID = l.getDefinition('V2').serviceLayerID
 
 
					
				
			
			
				
	GaetanPRU