I rang this company in the USA
http://www.psesuperchargers.com
and they can supply just the clutch and they will ship to the UK. They have two makes of clutches available one for $502 and the other for $400.
So for the record, if any ones magnetic clutch fails to work (engage etc) then this option is the best I could find.
If the bearing has wear in it you could replace just that, using this company,
http://bearingsdirect.com/products/...id=5110&prevaction=search&previd=&prevstart=0
However, after further discussions with the PSE company I discovered that if the shaft to which the clutch pulley is attached to has worn then unfortunately the compressor will have to be renewed also. The shaft is not part of the clutch like I first thought, it's part of the compressor housing.
Saying that, going back to what fredfloggle said and now that I have realized that the shaft can be more exposed, it is possible to have the shaft repaired by this spray metal technique and then machined back to original size.
I know this may sound like a lot of work but I and for people like me who are prepared to do the work it can be very cost affective and rewarding.
I hope this information will help others.
Cheers
BigD
Have you made enquiries in Germany ? Not only do many of them speak the Queens English better than Americans that is where most Kompessors were are sold in the first place.
Mercedes also have their own used parts centres like this one
http://www.mbatc.de/
adam