You may see two in a tank together but they are rarely "paired." What we see at LFS are mainly immature fish and not old enough to be "going steady." I think they are held two in a tank is more marketing then anything else. People are morelikely to buy two fish if they think they are a pair.

As clowns mature, the dominant or larger fish goes through a sexual metamorphosis and changes into a female fish. They are all born as males. The female grows quickly. Once this occurs they can become a "pair."

I had 6 oscellaris in a tank at one time. There was 1 female and 5 males and 3 LTA.