The dealers are the only ones with that information. Too bad they won't get it for you. It's bad public relations to charge so much.
The numbers aren't available to the public. The idea behind the code is that thieves won't be able to sell the radios they steal out of cars, so they won't steal them. If they could easily get the codes, this wouldn't be a deterrent.
Once you get the code, log onto the Honda owner's site:
Honda Owner Link
And you're the code there. That way, if you ever need the code and have lost it, you will be able to retrieve it.