I've seen a few ferret/weasel cels.  I know one
series is Rikki Tikki Tavi but those cels are
really expensive.  I've also seen a few from
unknown series on YJ.

Ferrets are wonderful animals, but like spinizuey
said, they are extremely high maintenance.  I have
had 3 of them and I love them to death.  But I
have also seen first hand how destructive they
are, it can become pretty expensive.  I don't
think a lot of people realize how hard they are to
take care of.