Sure, the Vitamin Shoppe has shelves full of the stuff. Magnesium oxide is almost useless as a magnesium supplement as it is not a very absorbable form of the mineral.
However, it is outstanding as a laxative. It fact, almost any edible form of magnesium has the same effect. Magnesium orotate, magnesium citrate, or even Epsom Salts will work. Use caution, the results can be quite dramatic.
Look at the ingredients label on Oxypowder for your answer.