I did the same research before posting. Couldn't find a flat, flat top for a Magnum. Are you certain your engine is a Magnum and not an older LA block?
I suppose you could always get some new pistons. The KB107s mentioned before are popular. Speed Pro has some inexpensive ones as well that I've heard are close to factory piston weight and don't necessarily require you to balance the rotating assembly. On my 5.9 Magnum I was lucky enough to just require a little honing to clean it up. I re-ringed the factory pistons and put in new main and rod bearings and bolted it back together.