"The" arrow at the time was P.O.C., period. Hill liked shooting P.O.C. What was available doesn't matter--P.O.C. is what he suppossedly used. I wasn't there, I just know what I've read about him. I'll try to find a referance.
I have seen references too. Not arguing that. Just sayin there couldn't have been too many arrow makers back in the day. And hickory trees didn't "quit" growing. HH made his own bows. And I have references, that he also made arrows.
He liked to snap shoot. Which I do not. Snap shooters usually do not fully ultilize thier full draw IMO.