The primary problem, I think, with growing larch south of the Mason Dixon line (and that seems to be roughly the line where they do well and they where they don't), are summer nighttime temps. Larch are happiest where temps dip below 70 F at night. They need the lower temperatures to complete their photosynthetic cycle. Higher temperatures at night inhibit that process. The constant strings of 75, 80 degree and higher summer nighttimes take their toll gradually.
I've tried to grow larch here in N. Va. for some time. Every time I try, the tree slowly fades away over two or three years, gradually weakening until there are only one or two branches left. It's happened more than twice. Others I've talked with here in Va. have had the same familiar experience.
The story, however, is exactly the opposite only 40 miles or so to the North of here. Larch grow quite happily in Maryland and beyond. The difference is only a few degrees in temperature and a few miles. Northern Va. and DC lie on the boundary line between two different climate zones--we can grow a mix of Northern and Southern species that isn't possible 50 or 60 miles to the North or South.--Unfortunately, larch isn't on the list this far south...
There is a solution that is more than adequate--grow bald cypress. It's a spectacular species to use and comparable to larch in the south. You also might look around you for native conifers--high altitude native species in NC include Fraser fir, pitch pine, Virginia pine and table mountain pine (pinus pungens, a particularly underused bonsai species IMO--also called Hickory Pine).