Helmets for big round heads

Apologies if this has been asked before.

I'm helping helmet-shop for a friend has a big head. Really. It's at
least 65+ mm around, and it is round, not oval, in shape.

He complains that even XXL helmets are no good for him because they're
made for people with oval shaped heads.

Any recommendations on big round bike helmets?

Thanks very much for any clues on this.

nycvelo