Need keycode for stereo as battery died now need code! ?

The battery died on my Peugeot 206 XSi 52 plate. So now we've started it up again it's asking for a key code? I attempted to contact the private seller and am awaiting response to call and email!!
Is there another way of finding it? I Have two keys one of which is blip fob and the other a manual turn. I don't know If any of this helps!?!
Any ideas, gratefully received x sarah