If the problem is recurring at 100000 miles, the diff housing is likeley to be worn as well as the clutch discs. I have replaced disc sets in many 35 rear ends, and the problem will still return after a few thousand miles because of this.
The type of locker which will replace the LSD parts in your existing diff are those like the Richmond Lock-Rite, Aussie locker and Detroit E-Z Locker. These fit into the existing carrier after removing the spider gears and clutch discs. You can order an Aussie from the US for under $300 including carriage, Richmond lockers are available from Quadratec etc.
At 100000miles you have to be careful, though, because of that diff housing wear. I had a problem with a Richmond locker in my YJ because the area where the spigot on the back of the spider gears runs in the housing had worn out at 40000 miles. You need to remove the clutch discs and see if the gear moves up and down in the housing, if it does, the locker and driveshafts will move about in the housing causing all sorts of nasty noises. If this is so, you will have to replace the diff carrier as well anyway.
The next step up is a Detroit locker, or if you want something a little less harsh, a True Trac. These replace the whole diff assembly, so you don't have to worry about the existing parts being worn (apart from the ring and pinion) but require professional installation unless you have all the right tools and knowledge to set up an axle properly.
Finally, you have manual lockers, the most popular by far being the ARB air locker, a complete assembly again, requiring professional installation and an external air supply and wiring to operate it.
