I have no idea on how to get the DLC's :(
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i got them with wii u usb helper on pc
If you have h shop you can download the dlc that is what i did.
But only for 3ds
hShop for 3DS or NusSpli for Wii U. Either HB App wil download and install it for you!
If you are using a Wii U use Nuspli they have Dlc for almost any game including Smash