To find out the radio code for your Honda Odyssey radio, take a look at the below website.
[http://www.freeradiounlocking.com/brands/honda-radio-code/honda-odyssey-radio-code/]
They have a guide on there which will explain to you exactly what you need to do in order to unlock your radio for free, it's worth a try as I've used this website a few times on different cars, admittedly not for a honda as I've never owned one but the method has worked for my other cars.