WordNet records no synonym and no antonym for mass production. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the production of large quantities of a standardized article (often using assembly line techniques)
Synonyms, antonyms and the broader and narrower relations for mass production come from Princeton University’s WordNet. Full sources and licences.