The War Games - Psychic Container

[elkad]

I think he used a acrylic baseball display case. Yeah, the acrylic may be a bit thinner, but its good for making a quick prop.
The alternative would be to find acrylic of the same thickness & cut the cube out yourself. Or go to Tap plastics & ask them to make you a cube with acrylic cone rods inside to hold the paper box inside.