There's a leather shop out on Boulder, on the opposite side of the Ness shop, less than a half-mile from them. Leather Headquarters, Leather Outlet... some shit like that. Shitty, little, one-story, white block building with a black sign with flames, next to a shitty used car lot. I go to Vegas twice a year, and stop in there every time I'm in town. Try them, they have a shitload of helmets and they're open on Sundays too. I thought there use to be a Cycle Gear in Vegas too, but maybe I'm thinking of somewhere else.
Hope this helps!