During my last post from monday and today I got an answer from the guys from Printrbot. They will send me the missing parts. I also found an ebay seller, that has the right hex nuts for the printer. So I ordered them too.
Today I received the hex nuts from ebay. So I can continuing the assembly of the printer. (The mail from Printrbot probably will take a few weeks.) I nearly finished the bridge module, as you can see in the image.
During the assembly today I got a certain feeling that I might miss a few screws to finish the assembly.