What is available for "service manuals" is in electronic, digital media. There are no official paper manuals by M-B/smart, nor any unofficial ones so-far from third parties (Bentley, etc.). Evilution (
Evilution - Smart Car Encyclopaedia) reports that what is available for W450 smarts is arduous to work with.
There is rumor that there will eventually be an electronic version made available to the public, but by subscription. $$s! One would hope that it would include the W450 as well as the current W451.
I have come across a repair CD for sale on the internet (don't remember where). When I looked at it a year of-so ago, it was for the W450. I have no idea of its useability, accuracy, currency, or authority.