I got my step bench years ago at a Service Merchandise store, which I think is no longer in business. A couple of places to try.. in my area, there are stores that sell used sporting goods. People bring in the things they don't want anymore, and the store buys them and re-sells tham as used. Check the yellow pages for that. Another place to try is ebay www.ebay.com
I did a quick peek there and saw several steps being auctioned off. do a search on the phrase step bench.
If you are handy, you could build a step yourself ...maybe. I think the used sporting goods store might be your best bet, since I don't see them in stores very much anymore. I know I love my step and am very glad I kept it. I also kept my exercise slide, but I am not glad about that.. at least not yet.