If it is not a current seasonal item, try yoox.com
If it is more current, try Japan's yahoo.co.jp auction site or www.rakuten.co.jp
There are a number of Japanese sites that have his items for sale and sometimes they will accomodate foreign buyers.
But, in this hemisphere at least, Chalayan can be a bit tough to find. But, if you do, it's great stuff. The quality is nice and the garments are quite comfortable. But, of course, you pay for that, in that the sweatshirt probably retails for $400 or so.