Parts fiche lists them as 10x38, but doesn't provide the pitch.  You should be able to figure out the pitch by checking the internal threads that the bolts mate with.  Each bolts also utilizes a flat washer and split lock washer.  Loctite is always a good idea.  The bolts are decorative items (i.e. chrome plated with no grade markings).  Best use a good quality stainless steel replacement if you don't plan on using OEM parts.  I imagine you should be able to find them in a good German hardware store.

LMK if you need more info.