I know what you're talking about. I'm not sure if they make that type of step anymore. I know when I was shopping around last year for mine, I saw that type on Amazon, but it had received quite a few negative reviews. Something about having to lock the risers in place and they seem to have a habit of slipping. You could check Amazon or Ebay. I can't even remember which brand it was, Step or Reebok, but I do remember losing interest after seeing that it was a pain to manipulate.
Good luck!