EDIT: Rocket_chick: http://pkmncollectors.livejournal.com/7244788.html
and Meowthcollector: http://meowthcollector.livejournal.com/5746.html
each have one. Rocket_chick got hers on Yahoo Japan for around 3.000 yen and Growly got hers for aorund $50 with shipping on a similar Japanese selling-stuff site.
On some Japanese blog, someone saw it at one point on Rakuten.
For those interested:
Product of this.
A link to buy the mini-microwaveable ones.
A link to buy something similar, Pikachu's head.