New or used bike? One should have been sold with the bike to record service history... or do you mean a service manual that the mechanics use? I got one of those from my dealer, there used to be one online.
There are 2 manuals. The OWNER'S MANUAL, and the SERVICE MANUAL.
The OWNER'S MANUAL is a booklet that fits under your bike's seat and is the thing Felix is referring to where you record services done if you do that.... This comes with the bike when new.
The SERVICE MANUAL, aka Factory service manual is a massive book you can knock somebody unconscious with, which includes procedures to disassemble and reassemble the entire bike, back to front.... These do not come with the motos, used or new. They are also about $80.