you see them on ebay

http://cgi.ebay.co.uk/LAND-ROVER-DEFENDER-late-2002-on-110-rear-differential-/290406989802?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item439d9affea

alternatively..buy one from Ashcroft transmissions

http://www.ashcroft-transmissions.co.uk/index.php?act=viewCat&catId=8

or get your old one reconditioned by Crown Diffs

http://www.crowndiffs.co.uk/diffs.html#recon_diffs

Kam diffs are very good --and they also make their own 4 pin centres.

http://www.kamdiffs.com/four_by_four.php?l=4_Pin_Diff&link=4_Pin_Diff442

Majority of diff failures are people spinning the wheels too much--when the tyre decides to get grip the plant wheels explode or pins break.... this is why standard cars [defender/disco] have 2 pin and more powerful vehicles have 4 pins--they came out after the V8 90 was launched in mid-80's...and the army had them fitted to 90's on the front line.

The other problem with powerful engines --the crown wheel is pushed out due to the torque and breaks the teeth on the crown wheel-- this is why diffs get 'pegged' --its a brass slipper plate which holds the crown wheel into the pinion drive so it cant bend out.

I knew 4 years of racing a Bowler Wildcat would come in useful on this forum :)

[dont get hung up on the 12 spline diff-- 24 spine shafts and drive members are cheap as chips]

i spoke to my man who breaks landrovers, no diffs to suit yours.  Says you may be better to go for a reconditioned one as cost is similar.

Hope this helps

Bren