Klaus is right of course. There are other factors to consider, for example in such a small space is there ventilation, space for a cooling fan etc. If each projector has a different space you will have to use different power supplies, especially if the airflow to carry heat away may be different in each case.
Forget using resistors, they would be bigger than the projector and run VERY hot. Your load is 24V at about 6 Amps so a dropper resistor would have to dissipate (240 - 24) * 6 Watts = 1.3KW !!
A conventional transformer would be too large but electrically the simplest solution.
That leaves only one viable solution, a switch mode power supply (SMPS) which you might find. Try searching for "240V 24V 6A" and see what comes up.
Brian.