Get a new CD Drive for it, preferably a 600-unit either internal or external. It is not that difficult.
If it's an external, any SCSI Drive should work on it. Just make sure you have the proper termination on it.
EDIT: HOW is the tray broken? If it is just the tray itself, you can replace that, it is not that hard to do. The problem is getting one that is from the exact model type. Like A Panasonic CD Drive tray will only fit a Panasonic CD Drive - it does not matter if it is IDE, SCSI or some oddball interface from the early days of PCs. So remove the Internal CD Drive and see who made it (Sony, Panasonic, et al...) and then go look for a similar old PC unit. Then remove the tray from that, compare it to the first and if it matches, swap it, and your Internal Apple CD Drive should be fixed.