b) Are there any instructors/examinarers in Germany, who I can revalidate my SEP (land) rating with. Mine has expired this May.
If your rating has expired, you will need a renewal not a revalidation. To do this you will need an ATO to issue you with a Course Completion Certificate before you can be tested; that does not mean you have to do any flying before the test. Any German Examiner can conduct the test in accordance with the EASA Examiner Differences Doc and should be able to get CAA permission to sign your licence.