There is good FAQ on pairing clownfish. It is in this forum in the sticky thread called "Clownfish & Anemone FAQ"
It will have information on how to pair up your own clowns. You can order a pair from the fish store but those are usually not breeding pairs, just 2 that happened to be collected together or noticed to be swimming together by the importer/wholesaler/distributor/store.
There is a good chance that a pair you bring together will breed as long as they are kept happy and given an appropriate envoronment to do so.