The seasonal event leather tags and bracelets are usually available at both parks. At Tokyo Disneyland it's the wooden shack in Frontierland opposite the Hungry Bear Restaurant. At DisneySea it's on the left side of the Indiana Jones gift shop in Lost River Delta. For the past few years, you could buy the Halloween leather tags at both. Don't know why Christmas would be different.
---------- Post added 11-13-2012 at 08:09 AM ----------
I just checked the page you linked to: in fact it has links to the shops in both parks I've just mentioned, so you can definitely get them at DisneySea.