They will still breed if you buy them seperatly. The clown that you have 1st will become a female so you will want to buy one that is smaller than the one you have so you dont end up with 2 females, 2 females will fight as once they turn female they cant turn back to males.
However maroon clowns are alot harder to pair. Most clowns if you get the same species will pair up fairly easy if you follow those rules but maroons can be very picky about their mates, i went though 4 males before finding one my female would accept.
If your intrested in breeding clowns i would suggest getting the book "clownfishes" by joyce wilkerson. Lots of good info on clowns and anemones.