I was hoping that someone would send in names ... however you are in God's stone country ... so many beautifully built dry stack walls. If you contact your local stone yard-I'd suggest several yards, especially ones that works with architects and masons primarily, you will be likely to find that special mason. To be sure good true dry stone wallers are even rather rare in your area, but African American even rare yet. Not all masons are "stone wallers". Those that deserve that term are a special breed, almost always very different from architectural masons. The difference? they live on their creativity and sense of beauty while an architectural mason, however good, depends mostly upon a different set of technical craft skills and a different set of aesthetics. The aesthetics are probably NOT perceivable by you when you quickly pour through their portfolio, but after you've seen a wall one hundred times (a couple of months) you will probably know what you sensed upon viewing but couldn't identify, i.e., the qualitative difference.
The interesting thing about the possibility of a0 an African American team is: A) they might have a wonderfully unique sense, perhaps with barely identifiable traces of the great stone work of Morocco, or Egypt;
and B)as a father and son team they may have really developed that special sense and style. Most of the great walling that can be found in the cities across America are traced to one or two family teams per city, so, in outdoor stonework you will find a style unique to rather small areas: different cities in Ireland or England, southern California, New England Vermont is different from New York or Philadelphia.
Good luck on finding the guys...