These are banned in the U.S., which is why you can't get them here. Apparently they've been deemed a choking hazard. There are also several threads about people who have gotten in trouble bringing them back, what is the risk while applying for Global Entry, etc., if one was caught with them, etc., etc.

On the other hand, if you like Ritter Sport, you can find varieties in Germany that are difficult to find in the U.S. (corn flakes!).