From the FAQ

"dealer only , go with your registration and photo id and the serial
#, model # and ref# off the top of the radio (remove radio to access),
they access hondanet and get it for you. Some dealers put a decal with
the code under the fuse box lid or in the glove box, 5 digit #.
Sometimes the original selling dealer will have record code by VIN#,
save removing the stereo."

http://www.tegger.com/hondafaq/faq.html