Yes, as caygad says, Pedersoli makes a double called the Kodiak, and it is available in .50, .54, .58, and .72 calibers through Dixie Gun Works and Cabela's. The one from Dixie has a straight-grip stock, and the Cabela's version has a pistol-grip style stock. These are beautiful, well-made guns and are quite accurate. Unfortunately, most states that have a special season for ML's force one to use a single-barrel weapon. This means you have to use your double during the regular modern firearms season. However, if you live somewhere like I do, where 100 yards is a long shot, using a double-barreled ML rifle in any season is no handicap!

Mine (a .54) shoots round balls like this @ 100 yards with 85 grains of Swiss FFg. Two rights, two lefts, R-L, R-L firing sequence.