There's no guarantee that a Clown will host in an anemone. I've had 2 pairs of Clown and neither pair paid the slightest attention to a BTA. But the 2nd pair hosted in a Colt Coral!
As far getting a pair - if you didn't get one straight off you can always wait for your current clown to grow a bit and then get him a smaller companion. Chances are fairly good that they will pair-up.