Where might I be able to download an older game?

I wanted always to try System Shock 2 and I can never find any place to buy it at so now I am resorting to maybe looking for some abandonware. I downloaded it off underdogs and followed the steps and ****, and when I push new game, it just exits me the **** out with a big old error message, time after time... So now I am basically lost... if someone maybe can give me some pointers about finding this game available on the internet (not buying, spent years looking for it, now I say **** it) or if someone has it nd can send me it via email it would be most appreciated! thanks