Too strong for a snaffle won't accept a pelham what bit can you show him in?

You shouldn't go up to a bigger bit. This horse needs training. If you can't train him, get someone who can, it'll be for the best. With training, you should be able to ride him in a snaffle instead of covering up his lack of training with a bigger, stronger bit. If you don't train him to go well in a snaffle, you will always be having to move up to a bigger bit, and he will develop bad habits, like evading the bit (if he hasn't already)

Maybe even try a bitless bridle

Try a Shank bit

try a rubber bit, basically try anything until you find one he listens to and likes

try not to pull hard, also remember you cant get a horse to follow you by getting a tougher bit, try retrainin him, a tough bit will only hurt or aggrivate him.