WeLoveFine offered a 10 inch plush balloonicorn, which they currently do not have for sale. However, you can pre-purchase a new smaller 6 inch version:
The plush is 6 inches with the horn included, and has a clip on its back for easy attachment to bags, backpacks, or anywhere else you want to put it.
Order yours now for $15.00, shipment expected in late March.
The Balloonicorn is an item from Team Fortress 2, that floats behind a player.
You can also get a t-shirt for $20.00.