The only way to get your own Famous Pinata is to get one sent to you by a game developer. They used to send them out to people who completed all 841 player awards in the game, but as of right now, they are not sending them out anymore.
You can still unlock the achievement if you find someone that already has a Famous Pinata and then be in their garden when they unpack it from a crate.
I have a Famous Pinata and still willing to help people out. Just send me a message on here or xbox live and I can invite you to my garden and unlock it for you.