Your description is a little vague. You might be able to find the stud you want at metric hardware place but you may be able to get something from Pelican. Try looking it up here:
911 Engine Catalog
Note: The stud length in the catalog (and Porsche's own parts catalog) is the amount of stud
exposed when installed not the overall length. If you buy the studs from someplace else the length with be the overall length.
-Chris