The LawBod has a separate collection of works on Socialist legal system of East Germany (1949-1990), shelfmark beginning German DR.
Gesetzblatt der Deutschen Demokratischen Republik 1949-1990 German DR 010
Entscheidungen des Obersten Gerichts der DDR in Arbeits- und Sozialversicherungssachen v.1-9 German DR 100 O12
Entscheidungen des Obersten Gerichts der DDR in Strafsachen v.1-2, 5 -16 German DR 100 O14
Entscheidungen des Obersten Gerichts der DDR in Zivilsachen v.1-7, 10-16 German DR 100 O16
Law and legislation in the German Democratic Republic 1959-1988 German DR 300 L10
Neue Justiz 1947- German DR 300 N30
Staat und Recht 1954-1990 German DR 300 S50
The book collection contains both contemporary works from the period, and works looking back at the legal regime of the GDR after it ended.
Subject searches in SOLO using "Law and Socialism" as well as "Law - Germany - History - 20th century" will help you pick up useful titles.