I'm also curious as to why the need to replace the cylinder head...
Fault codes only aid in troubleshooting. Often times a fault code is not even directly related to a part that fails. I'm sure they assumed one thing but once the tech dug deeper removing parts the real cause was found.
Please keep us d owners updated as to the outcome and what will be covered in the future.
I wouldn't doubt that parts may have to come directly from Germany, or at the very least from across the country from another dealer that may have those items in stock. The 335d is fairly rare here in the states probably <10,000 units sold here since they were introduced as '09 models.