I would try a Chemistry professor, or secondary school teacher. You won’t need a lot of the chemicals for just a demonstration. When you talk to them, be sure to have a couple books or print outs of what exactly you want to do. This will help them understand. A letter from the gallery would provide proof that you are not up to mischief. Also have an idea of how much of each chemical you will need. For example, I use about .75mL of bromine to 500mL water, and about a spoonful of iodine. You won’t need a lot of mercury, it will depend on how big the fume box is. I use 10ml of 1% gold chloride in a hypo/water mix.
Cheers,
chriso