I've tried to do all of this and I believe I moved the DLC correctly (all I did was copy them from the unbanned 3DS's "quest" folder to the banned 3DS's "quest" folder and import them) because I got a bunch of success messages when I moved the .arc files but the DLC quests aren't showing up in...
I've tried using mhx data manager, downloading the dlc on an unbanned 3ds, then transferring them to my banned 3ds, but that doesn't seem to have worked. I may have done something wrong though.