I had a 2005 Discovery LR3 V8(US Spec, imported to EU) and I could swear it had 3 diffs - at least the 4x4 Info screen would always show 3 diffs working independently when I was driving it offroad. Of course I might be remembering it incorrectly, but a quick search on google shows "genuine Land Rover Discovey 3 front differential" part on ebay, so I guess it must exist?
They have differentials on the front, but they're not "locking" differentials, they're "open" differentials, no locking capability at all.
Center diffs are for the most part (in Land Rovers) locking differentials, though some Discovery IIs had open center diffs and things like Freelanders use a viscous coupling in place of a mechanical diff lock.
Newer models have an electronically controlled locking diff in the gearbox (center) and an optional electronically controlled locking differential at the rear.
http://www.ebay.co.uk/itm/like/182246825443?lpid=122&chn=ps&...