I honestly don't even use my high level roulette for law. I use trials, high level, and low level for leveling alt jobs from 50-60, and just get law from expert roulette. When I was grinding for my main, I'd jump into tons of parties with people asking for help with first-time clears for Research Facility, Neverreap, and Fractal because bonus law is awesome that way. Going in a premade and grinding the law dungeons is also reasonably fast.