I don't know about them coming into the captive market. Keep in contact with any snake breeders you know in Bolivia.
As for information, here is Dirksen's translated page. It has probably the most information available on these two species.
http://translate.google.com/translate?hl=en&sl=de&u=http://www.anakondas.de/cms/front_content.php?idcat=15&ei=UnniSaedEJaBnAfw8LihCQ&sa=X&oi=translate&resnum=9&ct=result&prev=/search?q=eunectes+beniensis+dirksen&hl=en&sa=N&start=10

