The principal collection of German law journals in LawBod have shelf marks beginning German 300. They are then shelved according to the first word in their title.
Volumes from 2000 onwards are on Level 3
Volumes 1999 and older are on the Ground Floor.
There are law journals from German publishing houses in other sections of the LawBod, for example ZEuP : Zeitschrift für europäisches Privatrecht is at General 300 Z20 - so it always worth doing a title search in SOLO!
The Index to Foreign Legal Periodicals (IFLP) should cover the major journals published in Germany, as well as other civil law country journals.
To check whether articles about German law have been written in journals published in common law countries eg UK/US/Australia etc you will also need to use Index to Legal Periodicals & LJI on Westlaw eg.  Public Law 137 has an article on the development of German constitutional law.