I don't recommend DLC WADs usually, because they are large and can be difficult to install. What you should do is get on my Discord server, go to Alternity's spreadsheet, and grab Rudi's DLC Downloaders. There is a guide on my GitLab wiki on how to use them.
If you still insist on using DLC WADs,
@Larsenv has them on MarioCube, and he can help you with installing them if you contact him here or on RBC Discord.
Since the Wii is no longer being supported, I feel that I can safely say this here, as much of what could be downloaded on the Wii is no longer available to buy. If you want to download songs for the same titles on other consoles, check to make sure they can't be bought first, and if they
are available to buy, then I recommend buying those songs when you can afford it instead of trying to get them for free. If not, then you may ask in RBC Discord about what you can do to get those songs.