Back in the 50's, Dr. Wertham tried to interest other publishers in the book. When I was at the Library of Congress to see Wertham's files, I found letters indicating that he had discussions about both a Spanish and a Portugese version of the book. To my knowledge, neither of those ended up getting published.
According to a letter in Wertham's files, something Wertham wrote (I think it was an article and not the full text of SOTI) got translated into German without Wertham's permission. Since the article was published in East Germany, Wertham's agent indicated that he didn't have any options to remedy the situation.
I have some information regarding the current copyright holder for Seduction of the Innocent. If the publisher you know might still be interested in an Italian translation, have him/her contact me here or through the SOTI website (SeductionOfTheInnocent.org).