The combined online catalog of the two libraries in Bulgaria is an excellent source for identifying newspaper titles from the country. Since one of the two libraries is the Saints Cyril and Methodius National Library in Sofia, this should be the first catalog to consult. The holdings lists for the newspapers are very helpful. Search in Cyrillic characters.
Although the Academy does not collect Bulgarian newspapers at the same deep level as the National Library, it maintains a good research collection. The catalog often has detailed holdings for its serials. Search in Cyrillic characters.
The NALIS Union Catalog brings together the online catalogs of many research libraries in Bulgaria, including the National Library Ivan Vazov in Plovdiv, which has a good newspaper collection, the library of Sofia University, the largest university in Bulgaria. NALIS is the National Academic Library and Information System.