What are the metal shelves that stores like home depot use to display products?

im trying to buy some of them to make a stage on. they consist of 4 thick metal "leg" pieces with notches runing up along the sides and then a platform is made with an outline of the metal top that slides into the notches or is held in place with a large nut and bolt. then they place wood across the top. i dont know what they are called but im wondering if anyone knows where i could purchase some? and i dont mean any flimsy shelving, im trying to make a stage that could hold a couple hundred pounds (me, a few other people and my mixer/table) i also understand that i will need to get a few sections.THANKS ALOTTTT