Random but have you considered or tried anything like these for him?
https://www.amazon.com/Chew-Necklace-GNAWRISHING-Autistic-Long-Lasting/dp/B07VV9BCFT/
https://www.amazon.com/Munchewy-Sensory-Teething-Silicone-Toddlers/dp/B08SVV4XMF
https://www.amazon.com/Sensory-Chew-Necklace-Kids-Girls/dp/B08X67QXZ5
If you search "toddler chew toys" on amazon, they come in literally ANY shape, size, color, etc....