Well, this is the only place I found selling an otter; http://shorttailedopossum.tripod.com/. Check near the bottom of the page. Now, whether they are still selling it or not, that will need to be determined, oh, that and the fact that they want at least $4000 for just one parent raised otter, $4500 for a bottle raised one. (There is difference between the two)
Also, because they are basically completely endangered, the permits and whatnot required to get one would probably make it very difficult to start out and then rather troublesome to maintain, that is, if you state even allows you to try and register an endangered species as a pet.
:/
Good luck! I would love to have one, myself. That and a ferret. I lurv dem furry amnimals!