This must be for the 190E "Internationalle". What is your power plant... American or German??? I would be very surprized if you couldn't find a match, regardless of nationality, at NAPA.
If not, then maybe this is a job for Phil (at Mercedes Shop at the top of this site. The call is toll free, and he is fantastic to work with). I'd bet he could find you exactly what you're looking for.
Additionally, here's a resource for fasteners online:
http://www.boltdepot.com/
Good luck.
Jeff Pierce