Just to ilustrate Sandor's solution, here is the path where I finally found it. In my case, Netweaver 7.0 EHP3 for Windows:
Once the files have been extracted, the file LABEL.ASC can be found in this path. As you can see, it is compatible with the label requested by the Provisioning Manager ( SAP:NETWEAVER:703:EXPORT(1/3):*:* )
I hope it helps.