yep - that's a great site.
you can also check on forums like here and USMB - there are classified sections with people parting out cars.
Keep in mind rear differential failure is almost unheard of in Subaru's. I've never actually seen it happen and you would be hard pressed to search 10's of thousands of forum owners to find it either. Of course, if it leaked and ran out of oil it's dead.
If you have torque bind then it's likely your transfer clutches or Duty C Solenoid (automatic trans) or the Center differential (if it's a manual trans). This often gets mis-diagnosed by mechanics as a failing rear differential.