First off, it has to be made clear that the classification as subspecies "Boa c. mexicana" for Mexican Boa constrictor imperator did not carry through in the taxonomy.  Therefore we have to call it  Boa c. imperator, distribution area Mexico.

If one reads the classified section of a German society of herpetoculturist journal, one gets tempted to believe that true Boa c. imperator from Mexico are available like water in the ocean. However, if one attemps to buy a true "Boa c. mexicana", whose ancestors (all, not just one) really came from Mexico, it gets difficult.