Buying a Ticket at the Last Minute?

Is it common for tickets to be available at the box office for that day's show? I'm going with my friend to see Wicked Thursday night, and I hung out with one of our friends tonight, and she said she'd meet us for dinner beforehand. I had only gotten 2 tickets because I went through a broker site, and we discussed going, and I really just didn't think of it. But I'd really like to get an extra ticket, so she can go too or find a way for her to get one because she would like to go also. Anyone know if there's anything I can do?

they might have cancellations, i'd get there around 930am and check when the box office opens. u might have to wait awhile till tickets become available if any at all.