Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
If you can get a pc version you can use the wad file with Doom Legacy to play it on the mac. Or any other games with the doom engine (Hexen for example). Or you can play the shareware version
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.