It can be hard to get a replacement that will work for the sole reason that there are so many different versions of the cd-rom... and you need the same one you have right now. Last week I saw an ebay auction where they were auctioning off dead saturns (they had no idea what made them dead, they were just dead), you could prolly pick those up for $5 a pop if they are up still or if they got reposted (looks like they had shelves full of them). If you bought several of those you might get the one you need.
edit: alternately I do have another model 1 saturn laying around if you wanna buy that lol.