They are a rare drop from the rare game juggernaut. But spawning him can be a pain and chaining him even more so. White masks would be better than sage rings because it would leave open your accesory slot for bubble belts but you can simply cast bubble... though MP really does become an issue mid-fight.

I don't remember what level i was when i first fought Ultima, and second playthrough i was close to max. But the guide recomends level 47... though i wouldn't put much faith in that, Ultima can be tricky. 68 sounds decent enough, the only way to know would be to give it a shot. If you need a few more levels then coincidently, the great crystal is a great spot for levelling