For the XL - https://store.nintendo.com/ng3/browse/productDetailColorSizePicker.jsp?productId=prod10826
For the original - https://store.nintendo.com/ng3/browse/productDetailColorSizePicker.jsp?productId=prod410032
EDIT: Nvm, I see you're looking for the *new* 3DS, my bad. I would just wait until it gets released in the US, they'll probably have some on their site soon after that.
I saw on play-asia they're selling a stylus-leash for the n3ds and looks like it might come with a spare, but it's a little pricey at $12.99.Thanks I highly doubt they'd be able to have a part tho