Not sure about the Karcher, you will probably find a local supplier from the Karcher website or yellow pages.
For the petrol/diesel machines... what do you mean by servicing it? If you change the oil and filter regularly, and clean the spark plug once a year then you should be OK.
Have you got a specific problem?
Andy
PS - Chris - Still not heard definately from that job in the smoke we spoke about last year... it is still on the cards as I have spoken to the guy there, but they are struggling for cash at the moment. I don't know what is wrong with them, anyone would think that the building industry is suffering or something. I'll let you know when I hear something. A.