The Haynes manual for the 230/250/280 is ISBN 0856963461 and it is available on amazon.
There is also Mercedes-Benz 230 1963-1968 Autobook: Owners Workshop Manual (Autobooks)Veloce Press; (November 1, 2001)
ISBN: 1588500306 availabe through Amazon.
There is a Glenn's manual available too.
The Mercedes Benz classic center has most of the factory manuals available. I bought the CD-ROM (Volume 4 if I remember correctly) which covers the 113 and a number of other 60's series cars. It is not cheap (~$125 US ) but does contain a lot of information (all the BBB, electrical diagrams, maintenance, etc.)
Jonny B
1967 250SL Auto