Did you ever saw the other fishes chasing the clowns either during the day or during lights off?
If they were a special order and the clown were not tank raised I think that they must have been so stressed out, and that is probably why they aren't eating and dying.
Since we don't know how the fishes that just arrived at the LFS
have been handled during shipping(fish bag fell on the floor, the box fell or was thrown, etc.), that can cause a lot of stress to the fish.
I tend to ask the LFS
when they will be getting livestock and I wait a week after the day that the livestock arrived so that I don't get really stressed out fish and lessen the chances of fish dying in my tanks.
I spend almost near an hour looking at the fish that I plan to buy for any signs of disease or stress, etc.