You might talk to a custodian or school maintenance person to see if they have an air compressor. The physical education teachers and coaches all have something to pump up their balls. Hardware stores sell portable tanks that can be filled with air and carried elsewhere to fill tires and balls. Photo departments sell compressed air in aerosol cans for blowing dust off of negatives. If nothing else is available, maybe get a replacement hose for a tire pump from an auto supply place or bike shop. Role in a well inflated spare tire to use as compressed air.