I went ahead and bit the bullet and purchase some (LHS-1E) Engineering Grade Lunar Highlands Simulant from Space Resource Technologies. Link below. I ordered about 53kg and about 6 rocks. I'm part of a local robot club and thought it would be nice to set up some mini competitions on robots that transverse and or dig/transport the regolith. 

For now here are some images of the box made with 6" popular sides and a 1/4 plywood base. The sides were joined with dowel rods and the base as well with a grove for a cleaner look. It is about 24"x6' in size to test  differnt sizes of rovers and allow you to sculpt the regolith in valleys, hills and small creators 

https://spaceresourcetech.com/collections/lunar-simulants/products/lhs-1e-simplified-lunar-highlands-simulant