Rewiring Guzzini Brumbury lamp  

I have a Guzzini Brumbury lamp. It was working perfectly but the sleeve on on of the lamp holders disintegrated and new sleeves I have found (the plastic screw in tubes which hold the bulbs) which seem to be the same size do not seem to fit. I am not sure if it is possible to get sleeves which fit (and where from) or whether the whole fitting needs to be replaced (but it seems soldered on). Also, the rubber ring half way down the column has also disintegrated with age.
Does anyone know where/how it is possible to restore the lamp - do they sell spare parts now for example?
Thanks
Noel