Pike had a man who knew a man that could rebuild suspension units. It may be worth sending him a PM (The email address he has linked to this site isn't working properly)
That aside, I would be say that the brands that can be rebuilt by the manufacturer is greatly outweighed by those that can't. You can get basic coilovers from places like Japspeed for 'not a lot' and I would be more inclined to buy new rather than risk buying a set that need doing, unless you check first
Out of interest Dan, how much are OE struts? Maybe some uprated springs like Eibach could be an option.