If the show is sold out then the box office probably won't have any.

You'll be hard pressed to find any scalpers hanging around, with all the online options you don't see as many of those guys as you used to. If there are in-person scalpers, they usually are yelling about buying tickets even though they're selling (some sort of legal loophole? idk).

TickPick is a good secondhand site to check out. You see the full price with fees upfront, and tickets are verified.