Let's get creative! There is no need to secrecy of the hash. Pay celebrities to wear a dress with the hash printed on it. Influence a publisher to print the hash in all books for a year. Create a mystery about what the hash is about, so it is mentioned in lots of articles. Who is this eccentric billionaire that pays truckloads of money to spread these apparently useless 64 digits?!?
(Disclaimer: Method not applicable to normal people.)
Yeah, making many copies makes sense. But if you're doing that, it's way easier to just make many copies of the original message. In other words, just publish it as a book and be done with it.
Broadcasting the hash would make sense if the message should stay secret for some time. Although 500 years is rather a long time for a zero-knowledge proof.
(Disclaimer: Method not applicable to normal people.)