The chances of finding a world that would not kill the Boraal is miniscule. To find one in the time allotted during Homeward would be impossible.
This assumes that the Boraal star system is in the far off reaches of the galaxy and not in the interior of the Federation. If it is in the interior, then the surrounding star systems would be thoroughly surveyed, and the chore of selecting a suitable replacement world for the Boraalans would be no more involved than simply checking the records on the local neighborhood. The Vacca star system was a mere forty two hours away.
"There are countless M class planets in Federation space which can support the Boraalans
Half the population of Europe died
Yet when Amanda moved in with Sarek, half the population of Vulcan didn't croak.