Well it's refered to as "Diamond Plate". I was looking for polished aluminum diamond plate some time ago for a totally non-mame related project, but for the amount I was planning to use, I found the price to be prohibitive. I suspect that for a kikckplate though, it shouldn't be to bad. I'm not sure if there is Steel Diamond Plate available, but if there is, it should in theory be less expensive then the stuff I was looking at.
If you have any sheet metal dealers in your area, check with them, or do a google search for "diamond plate sheet", and you should find some distributors. (You'll also find a lot of links for truck bed liners too)
Hope this helps.