Option B would be to get bus drivers certified if the district owns the tractor. You will run into problems there depending on when the drivers are available on game days after their regular route is complete.
Option C would be to get a parent hired on with the proper license (assuming the district owns the tractor).
If the district doesn't own the tractor then you will be forced to rent both the tractor and the driver. I know that Penske out of Houston rents box trucks as well as tractors. Not sure where OP is. Final option would be renting a couple of box trucks that anyone can drive but that might be hard if you need a couple of 26 footers to offset the loss of a semi trailer.