So, it's been years since I've actually sat down and watched Spider-Man, the Toby Maguire film, and I got to thinking... Do they ever actually show where Norman's mask comes from? I remember where he gets the suit from, but not the mask.
We don't know.
At least I don't think it's ever revealed. He obviously took the Goblin suit from Oscorp and discarded the original helmet in favour of the new, scary, goblin one - but to my knowledge it's never shown where he got this helmet from.