This does sound like a sensory need. We bought this chewy at Amazon: http://www.amazon.com/gp/product/B006YBJ9XS/ref=wms_ohs_product?ie=UTF8&psc=1

It smells and tastes like chocolate. He also liked the lemon and orange ones from the same manufacturer. They have two differently textured sides.

There is a whole industry for this type of need and I was surprised to find they had chewy pencil toppers, vibrating chewies, special chewy jewelry (necklaces, bracelets)and more.

My son found tremendous stress relief in chewing these items. It rather shocked me how he responded when I gave him one. He wore his around his neck tucked in his shirt or attached to a retractable badge holder clipped on his pants pocket. They did help him focus and relieve stress that needed a physical outlet.

Hope you can find an appropriate outlet for your son. I believe understanding that it is a need helps in finding the solution.