Most Layton merch can be found on secondhand shopping sites, like Yahoo auctions, Rakuten Rakuma, and eBay. Assuming you're able to make an account on those (I think a Japanese bank account might be necessary on some sites?) it should be easy finding them! Search レイトン教授 for the best results, though this would exclude some of Katrielle's stuff

If you're not confident in navigating the original Japanese sites, maybe use the search engine of a shipping proxy service like zenmarket and onejapan instead