Yes, secondary data can be collected from published as well as unpublished sources. Published sources are in the form of reports and newspapers that are provided by government, private and foreign publications. For instance, Reserve Bank of India bulletin and Indian trade journals are sources of secondary data.
Unpublished sources, on the other hand, include private records of scholars and research institutes. Sometimes, the unpublished data collected by the government or other organisations can also be used as a source for secondary data.