I have never found a portable charcoal/gas combo grill. If they did make one, I wouldn't buy it--the air flow requirements are too different for the types of fuel. Gas grills require a lot of air flow to burn, but charcoal grills should be nearly airtight when closed up in order to control the heat level. (too hot=close up the vents a bit and snuff down the fire).
IMHO, get a Weber Smokey Joe, it will do everything, and are a very well built little grill..
If you want a non-portable grill for home use, however, this one is pretty awesome.. Just add the side fire box, and you have a charcoal grill, a texas style offset smoker, and a gas grill for flipping burgers all in one unit.. I have the smoker portion with side fire box, and love it.
http://www.chargriller.com/duogrill.html