Set up Engineering in Wandsworth.
MH Racing in Wiltshire.
Maxton.
Any suspension specialist will rebuild a standard unit,its wether or not its cost effective if too many parts are required.Have a chat with them.A standard unit in good condition,set up correctly is perfectley adequate for road use and trackdays.With 99% of folks claiming to need "uprated" suspension,its a case of egos writing cheques that their ability cant cash.