The only legal way to obtain these keys is to . Distributing these keys online is a violation of copyright, which is why you won't find an "official" download link from the emulator developers. The Standard Dumping Method:
If you've recently fired up the Citra emulator to relive some 3DS classics, you likely hit a wall: the dreaded "encrypted ROM" error. To play many commercial games, Citra requires a specific file— aes_keys.txt —to decrypt and run them. citra aes keystxt updated