No radio code for Opel

I bought a 2004 Opel Astra still in very good condition but after replacing the battery I find out that Delta don't keep radio codes for older cars, That is really bad because I got a radio code from Mercedes 2 months ago on a 1984 model and the same with BMW if they try to copy do it properly that radio don't have a screen its part of the dashboard now I have to throw it away.