From PinataIsland.info, the Viva Piñata wiki
Famous pinatas don't look any different from ordinary pinatas. Outside of having a different tag (since it wasn't hatched in your garden), it's not really possible to distinguish a special pinata from an ordinary one.
Ways to obtain a famous pinata
|Although the game will still prompt you to contact the giant Goobaa for a reward (after earning all 841 awards), Rare is no longer able to send out famous piñatas.|
- Trade with someone who will lend or give you one. The TiP Trade forum is a good place to ask or to look for threads where members offer to help others with the achievement.
- Visit a friend's garden online, and have them unpack a famous pinata while you're present.
Ways you can't unlock the famous pinata achievement
- It isn't possible to hatch a famous pinata. Although some pinatas are stars when they're born, or become superstars as their value increases, this is not the type of fame that the achievement is looking for.
- It isn't possible to scan a famous pinata. Using the camera tool to create a Piñata Vision card of a famous pinata, will cause it to lose its Rare fame.