This is the cheat code database which i know is the latest i got thats for the R4..So you can put this in the cheat code folder in your DSTT and activate away.Im positive you can find the cheat you've been looking for, for YuGiOh 2008.. Enjoy!
I don't have a wii u anymore to test it myself, but if homebrews are not visible on the wii u menu I think you can press L + R + minus to open the plugin menu, there should be an option called "homebrews on wii u menu" or something similar