You can actually find many larger boas in rescues, for adoptin.
It gets them out of needing a permanent home and typically have many possible health problems eliminated during their foster home visit.
Larger snakes can also be better adjusted to humans, meaning less stress and problems in feeding etc.. (not all, but many)
Another advantage to getting a larger boa, is in the caging area.. needing to supply one, possibly two cages for its entire time in your care, vs a baby, needing several cage size upgrades along the way.
