My son is too big for diapers

So my son is 2 1/2 and 50lbs.. hes not fat just a big boy and very solid. He isnt potty trained yet..I'm having trouble finding diapers that fit him. Hes too big for the biggest size diaper as well the biggest size pull ups. Are there any other options? I'm really struggling finding something that will fit him.

And yes, we have been trying to potty train him. We are first time parents, we are trying but it is hard.