I believe it's possible to adopt one already in captivity, but I think you have to have a USDA license to do so, AND they have to approve the transfer at the federal level, but I've been led to believe that they almost never will.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry