An Anemone!!!! Now here is where the challenge begins. You obviously need to get one that your clowns will host in. Good luck on that, it can be hard especially if the clowns where tank raised. However its not impossible nor unusual to get it right.
I have had bought 3 anenomes for people and 5 different tank raised clowns. In each instance, the clowns went to the anemone within a couple of days. In 2 of the instances, the clowns feed the anemone too... I guess Im really lucky.