Open the Object Editor and click on the Gryphon Aviary. Then find Model Used (or something like this) and double click it. A window will appear and in custom path, you may find a path. Copy it (Ctrl+C). Then, in your skin paste the path. And don't forget to type .blp at the end. If you cannot run Wc3Viewer you will have to use this way.
-Rui