If you notice, the US has a lot of safety regulations for toys. This translates to differences between the TDS and US version in the details. For example, The Cannery Clothing Co line, uses buttons and snaps, which might not be acceptable in the US (due to choking concerns). The recent US Pajama set, opted for embroidered buttons vs real ones.
You'll find that Build-A-Bear provides for many dressing options for Duffy in the casual clothes category. Which also work for young children.
Adult/Child clothing that feature Duffy, and I do not recall seeing much in Tokyo.