Red Tail Boas are classified as follows:
Boa Constrictor Constrictor (BCC)- These are the "true red tails." These are generally the largest in size and maintain their red tails into adulthood. They come from:
Peru
Brazil
Venezuela
Suriname
Guyana
Boa Constrictor Imperator (BCI)- This is the largest group of boa constrictors. They include the boas from Central America:
Colombia
Panama
Costa Rica
Nicaraqua
Mexico: Tamaulipas, Tarahumara
and the insular islands:
Hogg Island
Caulker Cay
Crawl Cay
Corn Island
Pearl Island
Boa Constrictor Amarali (BCA)- Bolivian boa constrictors
Boa Constrictor Longicauda (BCL)- These come from the Tumbes region of Peru. They are also known as the Peruvian Long-tail Boa, as they have a higher scale count from their vent to tail tip, than the Peruvian BCC.
Boa Constrictor Occidentalis (BCO)- Argentine boa constrictors.
It is best to research each of these, as they have different sizes, colorings, and growth rates. Here are a couple of websites to help you get started:
http://www.cuttingedgeherp.com/contactinformation/
http://www.riobravoreptiles.com/index.htm