Following. I have a 2 year old autistic chewer as well
Have a look into a gummee glove
https://gummee.life/collections/special-needs-glove?_gl=1*17ft9a1*_up*MQ..*_gs*MQ..&gclid=CjwKCAiAlPu9BhAjEiwA5NDSA0CsC7iGe9M2rvH8MLbihWuyYkbdsYK-hW8CoqBSAn4hIftRLfcwMhoCjlUQAvD_BwE&gbraid=0AAAAA-nUTk3y5X7Fr3lTJeg97JeTHwfGc
My 3 year old daughter is the same. I've purchased different types of chew toys and necklaces and she usually discards them to go put something else in her mouth. I will say keep trying to give it him and redirecting. The chewy necklaces i tried a month ago is now working. She's using it instead of throwing it on the floor. The other thing that worked is vibrating teachers. The one I bought worked really well until the product itself stopped working. I've also seen suggestions online to give them things with strong flavors like lemon or something spicy to help them get the sensory input they are seeking.
Hiya hun my son who is almost 8 is Sen and he’s always chewing, I also work in a nursery for children with Sen who also chew!! Have you tried chewy necklaces or bracelets? You can order them online and they come in many different designs and shapes/colours etc!! X