Hi Nat,
A step (used for step aerobic workouts) is different from the mini-topper or stepstool/toolbox.
The mini-topper (as seen in Cathe's videos) is made by converting a regular size aerobic step into a smaller/mini version, and purchasing extra risers. Many of us who either cannot or did not want to tackle that project (I had trouble with Lego's as a child, so building a mini-topper was never going to happen!) purchased a stepstool/toolbox. It looks like a rubber step stool (like the kind you might keep in a kitchen for reaching on top of high shelves), it's about 13-14in. high, and most of us use it for leg presses, step ups, back lunges, etc. It's only wide enough to stand on with both feet. Neither the mini-topper nor the stepstool/toolbox could be used for step aerobics. it's too tall and too small width/length wise.
I found my stepstool/toolbox at my local hardware store. I'm sure if you went in to your local hardware store and explained you were looking for the "Rubbermaid combination stepstool/toolbox" one of the sales people would know what you meant. That's the only way my hubby got it right!
They didn't actually have it on hand, they ordered it and I had it a few days later.
Maybe others will have some alternate store suggestions.
As for a step (aerobic), I understand that "some" K-marts are carrying a Cathe video and small aerobic step package. You may want to check that out. If you don't mind paying for the full size step, you can find them online at several places (fwonline.com,fitness1st.com are just 2 sites), they usually run about $80. + ship/hand)
Donna