Question:

or it's just sold in tokyo disney sea?

Answer:

Okay, after doing a bit of research, it does seem like they do only sell it in tokyo disney sea.
The three stores within tokyo disney sea that you can get it from are:

-Aunt Peg's Village Store:
http://www.tokyodisneyresort.co.jp/tds/a…
-McDuck's Department Store:
http://www.tokyodisneyresort.co.jp/tds/a…
-Galleria Disney
http://www.tokyodisneyresort.co.jp/tds/m…
(this info was directly taken from Japan's disney sea website)

This website, in english, says the backstory of shellie may and duffy and why it's only sold in disney sea:
http://supermerlion.com/duffy-the-disney…