Abbreviation for:
Huáng Xiànián 黃夏年, ed. Mínguó fójiào qíkān wénxiàn jíchéng bǔbiān 民國佛教期刊文獻集成．補編 (Supplement to the Complete Collection of Republican-Era Buddhist Periodical Literature), 83 vols. Beijing: Zhōngguó shūdiàn, 2008.
This is a supplement to the MFQ, which was published two years before this collection.
The Digital Archives at Dharma Drum Buddhist College developed a search tool for the entire collection, which covers both sets.
Here is the PDF of an essay that discusses the structure of this collection, the history of its compilation, and tips on how to use it.