You'll find a large contingent of "folk" harpers at the Grandfather Mountain Highland Games; there's also a large number of harpers in Atlanta. You can find out what sorts of harps are popular and what players want and need if you'll spend a little time with the players themselves. I'm almost (almost!) sorry I don't live in the US anymore, since I was based in that area and would have been happy to give you some advice and help you with contacts. As I play the less-well-known wirestrung harp, my personal experience probably will not help you very much, but my favourite US harpmaker is Atlanta-based Robert Cunningham, who made two of my big wire harps and continues to produce fine instruments.