I'm looking for a new one, too... specifically the new black and silver ones . I tried writing an e-mail to the step company, but I never received a reply.
Here's the link for the original step in black and grey - just like Cathe's. I ordered mine from here (it was a Christmas gift from dh!) and their customer services was really good.
Not black and grey, but I just bought a club step--just like the one Cathe uses in her step videos at Walmart. It was only $58. I've never seen them cheaper anywhere else.
It looks like the link below sells just the top for the step as well, which is good to know. Mine seems a bit soft and I didn't think I could get just the long top without risers. Kind of cool!
If you can't find one at your local Walmart store they have them available on their website. Of course, you have to pay shipping, which can be a bit expensive. Then again, maybe your local Walmart can order one for you.