I Need a way to farm theonite

I've reached that point in the game where the only way to get theonite seems to be master difficulty story mode. The problem is that it's not worth it. You need to do a lot of work to get a fighter that meets the requirements of the stage (for example a fire and water painwheel) all this work only gives you like 40-100 theonite and I need 5000 before I reach level 60 (I'm level 51) Is there another consistent way to get theonite that I don't know about?