Originally Posted by Technohead
Find a whole used axle and then rebuild it. Id recommend starting with a high pinion from a 96-00 XJ.
^What he said. You might get lucky enough to find one with 3.73 gears, assuming that's what you need.
If you keep what you've got and buy the axles, u-joints, carrier, gears and all other needed parts separately; you'll have alot of $$$ into a Low Pinion D30 axle.
Find a High Pinion D30 with the Spicer 5-760x u-joints and rebuild it. If you're unfamiliar with setting gears, rebuild the rest of the axle yourself (easy part), and have a reputable shop rebuild and/or re-gear the carrier.