This design is graciously provided by Nori L. of WA. She built the grinder from scrap materials (PVC tube, roofing nails, belts, gears, pulleys, and an old lawnmower motor) and is able to grind large quantities of scrap. She is currently coverting an old plant shed to house the grinder and materials.
Unlike having free bags of cross shredded paper to make Papercrete, EPS-crete requires fine ground scrap styrofoam, the stuff left over from protecting products during shipment.
Unless you have access to a factory that gives away the waste scrap, as the Paraqcrete inventor does, you need to shred your own.
There are many expensivve, and huge, shredders working commercially at schools, companies like Walmart, etc.. What you need is a simple way to grind up what ever you get for as long as you need it. ( And with your own grinder you could rent it out for others to shred their own scrap foam.)
The design for a simple shredder made from left over and scrap parts and materials is offered here as my gift. Build your own, or start building them for others.