If they're redoing the cafetorium, and the gym is picking up extra events that would normally be hosted there, making the availability off, that's one thing. If you can't ever have concerts, ever, that's something else altogether.
If it's a temporary issue, this is on you for not scheduling your concerts before all the dates were taken. If this is "how things are" then absolutely look for a new position, because they don't value you in your current one.
Consider having concerts on the weekend if it's just an availability issue. Maybe you can have a Sunday afternoon holiday concert. Many programs do this.