Like Clifton said. It's somewhere in the flooring section. I remember somewhere near the "please wipe your feet before you come in" welcome mats. It's a thing for one step at a time. Should cost about a buck. Probably enough material to make two big old mud flaps. Measure and make a template out of paper. When your happy with the fit and coverage, put it on the mat and cut around it with a utility knife. Remember to allow about two or three inches of fender/mud flap overlap, where you will attach with a zip tie.

Yes... as long as you don't hit a pothole, ride over a speed bump, hit a small rock or branch, or go down a curb (even when off the bike). The great advantage of a flap is that it's flexible. Mine is about 2 or 2.5 inches off the ground, which is just high enough so it doesn't scrape most speed bumps and potholes.

I would like to add to the list.

Ride in deep snow
ride in mud
ride over a log
try to roll your bike backwards up a curb or a step.
and many others including...
Stand you bike up in the ice for a photo

This flap goes in as much 6" deep snow as possible. And works OK in 12" deep snow, unlike the engine.

http://img265.imageshack.us/img265/1272/hpim3445ss0.jpg