I just bought a Sony Personal Audio System RDP-XF300iPN. I discovered that its docking system is only compatible with the iPod 5th gen and not with my iPod 4th gen. Is there any way or anything that I can get so that I can still use the docking system?

I really like the Sony Audio System RDP-XF300iPN and my iPod 4th generation still works via bluetooth, but I would like to use the docking system especially to charge my ipod. I know the RDP-XF300iP has a docking system that is compatible with the 4th gen, but it has been discontinued and I cannot find it anywhere. I didn't know if there was an adapter that i could possibly use (similar to the lightning to 30-pin Adaptor for the 5th gen)?