Found 1 pathways with zero (PubMed) references
http://www.wikipathways.org/instance/WP472_rr117324 'Phosphatidic acid and phospholipid biosynthesis' in Saccharomyces cerevisiae has zero references;
More details at https://wikipathways.github.io/WikiPathwaysCurator/ReferencesTests/atLeastOneReference