help!! Going crazy looking for story

I´ve been looking for a short story I read many years ago, I thought it was Bradbury´s but I haven´t been able to find it in his books. I am obssesed with finding it now, like when you try to remember a name or a word and can´t think of anything else. I´ve asked well read friends, visited bookstores,hassled sales people, disturbed my poor aging father who had to look through his whole library, cause I WAS SURE I read it at his home, but nothing. Sometimes I think I dreamt the whole thing up.
The story was about a secret society that dedicated itself to wishing harm on others. It begins with a representative of the society calling on a potential customer and explaining how they work: thousands of members concentrate on wishing misfortunes on someone specific, one of the clauses is that the person must know that thousands of people are hoping something bad hapens to him/her. The customer, who remembers his life long sworn enemy, is skeptical, but the representative offers statistics, hard facts until the customer (and the readers) is convinced that this is the best revenge ever. But when he says that he wants to hire their services against his enemy, the representatives says that it´s too late, that his enemy has already hired them and that the society has already begun to wish him harm.

If anyone can help me I promise I will wish him joy and happiness and success and good health and material riches, as well as unlimited affection by family members and stranger alike.

Thanks!