Just buy a small one and add it, they will probably pair up. I had a pair, one jumped, and then I got a new one. It paired with the new one too, and then I had a house fire and lost the tank and all the fish except for the one clownfish I originally had, which was flopping in a little puddle of sooty water in some sand. I had the LFS hold him and now that I have my new tank set up he is paired with yet another. You can see them both in my avatar pic there.