The Littman Library has six volumes (v. 2, 4, 5, 6, 7, 8) of the 1931 Newark Sanborn Maps in the Rare Book Collection.
Volumes 4 and 5 are digitized.
Newark Sanborn map, v. 4 (1931)
Newark Sanborn map, v. 5 (1931)
Volumes 2, 6, 7, and 8 are not currently digitized. Refer to the Sanborn Map Key to locate the area of Newark you're looking for, which will then tell you what volume to look in.