Ó Flaithbheartaigh and Ó Dubhda would have obtained them from Dubhaltach Mac Fhirbhisigh, whose family created and preserved the book.
In this context, Ó Flaithbheartaigh and Ó Dubhda obtained the manuscripts from Dubhaltach Mac Fhirbhisigh, who was instrumental in preserving his family's literary heritage.