Enter "Psyllium Husk Powder" into Google or Froogle or choose your favorite health food supplier. Most carry it in the bowel cleansing aisle.
As for what is is enter Psyllium into Google Images. There are are few other names for it. All I know is that it is a plant.
You can get it with or without herbs you can also get it not powdered.
My personal favorite is Yerba Prima brand. Plain and finely powdered.