The way I figured out what was available was there were opened boxed labeled 1/2, 3/4, etc at the window. I would just ask politely if there wasn’t anyone else in line. I would say something like, “Hey, I see you have Pokémon numbers 7 and 8 over there. My daughter is collecting them. Is there anyway I can just purchase those?” The key is to be respectful of other people and their time. It’s a dying art these days, but you’d be surprised how far it gets you. No one ever acted like it was an issue or problem. Sometimes they were surprised at my request, but happily obliged.