Many don't have a clue about the wavy mulchers. They'll tell you they don't exist even. They do. Just tell them you want the wavy mulchers that come with the mulch kit for a 910, 920 etc for the same sized deck you have.
I don't have time right now, but you can look up the blade part number on JD parts .com. If you can't find it, post what size deck you have and if I get time later, I'll look it up.