Correct me if I'm mistaken, but Professor Layton and the Curious Village was never released in the Dutch language. I know there is a fan project currently underway on GBATemp to create a translation for the Netherlands, but nothing official. It'll be pretty difficult to create a Dutch cover; the text will all need to be removed, translated, and replaced; the title and spine artwork will need to be erased and heavily customized; and the region icons will have to be removed and replaced with Dutch info. I'm not even sure there's anyone on the forums here who speaks Dutch, and I don't think there's a PAL version of Professor Layton on the site to use as a basis for the redesign. It's no wonder why you couldn't find one online, this is one of the more challenging requests I've seen. Good luck!
EDIT: I just looked up the GBATemp project and I see you're helping do the translation over there. Perhaps if you can provide a translation of all the text on the official PAL cover, someone will be able to use that to fulfill your request. We'll still have to track down a high quality PAL scan to use as the basis of a custom cover, but the translated text will be a good start at least.