There is quite a bit of ultralight gear for sale at a few places on the AT, like at Neel's Gap and NOC.
Stehekin Valley Ranch, about three miles off the PCT in Washington State, had tarptents, alcohol stoves, and quite a few products from Golite there, as well as a few other things that I would associate with skinny gear.
Retail outdoor gear is a tough business in general, and honestly the ultralight part is even more ugly. It has nothing to do with a lack of demand. It has more to do with the fact that an ultralight pack that costs $125 will require the same amount of floor space as a $400 pack, and arguably more time and effort on the part of the staff to match customer up with product. The other problem is that you'll have a hard time attracting any experienced ultralighters to your store because they will probably be much more willing to buy over the internet, and much more aware of alternatives. Similarly, because there are so many cottage-industry companies in the ultralight world, to have a decent selection your store will have to have direct relationships with quite literally dozens of companies. Most outdoor stores order through a wholesale distributor, so they really only have a relationship with one or two suppliers. That can take time and cost money.
Competing with the big-box retailers locally and internet sales is going to be tough. You need to offer something really special in order to build the customer base and reputation that would give a retailer the traction it needs to survive. Some retailers have done this through connections with outdoor education programs: people who don't have the gear for the classes are handed a shopping list and pointed at a particular store.