POWDER PAINT: it seems that some health and safety busy body has decided that powder paint is unsafe. Your local schools may thus hold stocks of the stuff which they are no longer allowed to use.... scrounge it, they may be glad to get rid of the stuff.
AH, but, it's not that good to use - it tends to rub off on things, including school uniforms.
Another AH BUT -- buy some white wood working glue, mix the glue, the paint and water together with a drop or two of washing up liquid, and you make acrylic paint, which doesn't rub off on anything. (Clean your brushes thoroughly as when this stuff dries it will not move.)
If powder paint is unavailable, get bottles of premixed water colours and mix these with white glue