Is there a box office there to purchase tickets for Saturday night's Apathy/Celph-Titled show?

You typically pay at the door

There is no "box office". But you might want to check with who ever is having the event to see if you can pay at the door.

Sometimes depending on the artist you can purchase tickets thru ticket master

I don't believe so. All the shows that i gone to there you have to purchase tickets prior to the event