Gardner "Small Arms Makers" 1963 has nothing.
"Der Neue Stockel" by Heer 1979 shows:
B. Zubrod Homburg vor der Hohe, Hessen-Nassau/D, ca 1840. QO . He also shows 3 more Zubrods ( H.C. ca 1780, J. ca 1740-1770, and Phillip ca 1800, all from Cronberg (Kronberg)Hessen-Nassau/D.
No "Lubroo" is shown in either international source. Look carefully at the barrel signature and I'll bet the "Zubrod" is correct with some missing silver inlay.
No other info is in the book for these smiths. Bill Paton