Just use normal metal cutting bits from you local Home Depot or whatever hardware stores you have locally. As MountaineerGreen[n] suggested, start small and step up. But dont start too small or else you'll just break the bit -- it all depends on how thick the section that you're drilling through. Of course, the thicker the section, the larger bit you want to start off with as a smaller bit will break off once the bit develops too much friction from the thicker walls and your hand oscillates from the motion.