Unfortunately I will not actually get a piece of it - he just wants a pen from this type of wood. I'm guessing that even if I had a piece of driftwood once I turned it down it wouldn't look like that. I may have to resort to treating it after turning down to size.
Turn most any wood down to size, use some coarse grit sandpaper to give it texture then stain it gray. The only way for it to be natural is to leave it out in the weather about 3 to 4 years after turning it.