it would be a safe bet that most single wild caught fish are 75% female. if you do get a wild caught clown you are bringing in a whole slew of parasites, fungus, virus's and bacterial and could possibly get the whole tank sick. i would try to find a tank raised fish under an inch and have it shipped to you. this is the only way for you to know it will be safe.
example. most male clowns are tiny in the wild. if they are seperated from the female for more than 15 days, it already turning into a female and it cannot stop or revert back. with diseases or a war on your hands you could be possibly looking to buy another fish, or a pair for that matter. i never had a problem with any clown hosting in a nem WC or TR. it just takes time and patience.
good luck to you.