How do I find the code for the radio in a Honda that had its battery disconnected.?

I have a Honda Civic (2000). In order to clean the battery connection I had to disconnect the battery. After doing so, the radio stopped working and is asking me for a code. I bought the car used so I don't have the original paperwork. Is there another way to find the code other than buying a new one at the dealership?How do I find the code for the radio in a Honda that had its battery disconnected.?You were given a card with code, should be among your papers or manual. If not dealer is only one can give it to you.