Here is a set of chewable sensory necklaces. Make sure to inspect them frequently and replace them when they start to get torn. I personally do not give them the koala one because it has pieces that might break off too easily. https://www.amazon.com/Sensory-Necklace-Silicon...
Sounds like a chewy is in order. Check out especialneeds.com for different types. He must have that sensory need to chew. My youngest son chewed on toys.