I do it by hand at home. On commercial projects in the past hopper-type spreaders have been used by adding vibrators to the side of the spreader. Those with acerage use a lime spreaders successfully. When lava sand is mixed with humate or some other dry amendment or fertilizer, it will flow easily through most any spreader.

Lava sand absorbs moisture and is hard to spread damp right out of the bag. Open the bag and let it dry out before you spread it.

Maybe this tip will be helpful. We used a commercial broadcast spreader that we purchased at Foreman's to spread wet lava sand. The trick is not to overload the spreader and to keep it loose by bouncing it as you walk.