I can't imagine anyone complaining that their Alp doesn't grip acceptably, but I know that one day someone will have so much grunt that they'll be looking for a competition Gripper LSD and no one will know where to get one.
Well, In retrocar magazine there's an article about DR Engineering and their competition diffs and an advert by them listing various ones.
They list a Renault 25/30 as GBP 700.
Their number is 024 7640 4614
and their stuff is on the
www.racecar.co.uk/gripper web-site
Cheers
Alpine A110, Renault Safrane 2.5dt, Hudson Kindred Spirit (Renault powered), transAlp (Honda) and Ducati Multistrada