Yeah, unfortunately the only DS flashcard I have is an old Acekard2 that has been blocked on the 3DS. I saw there was a way to get some DS flashcards working on the 3DS but that requires that you already have a way to install CIA files. I still think this method has potential without any Gateway or DS cards though.
I got a DS Flashcard ~ 2 Years ago. This one works without any problems.
I'll try it after I formatted my EmuNAND
btw. this is my Flashcard:











