Need old version of Xamarin Studio and Mono

Hi,

Recently I had upgraded Xamarin and Mono, etc and there are some issues cropping up in the program which is just not ending. I have decided to downgrade to what the version of Mono and Xamarin studio I had earlier, but where can I find all the versions of Mono and Xamarin Studio? And how will I know which version of Xamarin Studio is compatible to which which version of Mono?

Thanks.