Welcome to the forum Rok, I don't know where you can find maintenance history for your car except from your friend.
You can request a Data Card from the Mercedes Classic Centre (see below)
The card will tell you quite a bit about the car. You need to provide Tom with the Vin number, your drivers licence and proof of ownership (you can scan the foregoing or take a close up picture).
Contact Information for Tom at the Classic Centre. Once you become a member here you will have access to the Technical Forum (it is worth it's low membership in gold)
Tom Hanson
Supervisor, Parts Operations
Mercedes-Benz Classic Center USA
MBUSA, LLC
9 Whatney
Irvine, CA 92618
949 598-4842 direct
949 598-4870 fax
Thomas.hanson@mbusa.com