Balance has never needed a Convert, it has all of the spells it needs. If Balance faces a storm Boss, he can use a Pure Balance spell. If he faces a Balance Boss, he can use Spectra Blast or Hydra. The only thing that can really stop a Balance wizard is a Balance Dispel or a Tower shield. That is what makes this Wizard so unique, he has a spell for everything, and doesn't have to waste the time putting up converts.
There should be a sun or balance spell called Colorful Prism, and it converts any spell into it's opposite school, but doesn't have any effect on balance.