This first link may be a useful starting point for holders of an Oxford SSO
The journal below is held in the Law Bod
Anuario de historia del derecho español 1924 - 2008/9
Law -- Spain -- History
Feudal law -- Spain
Note Check the location of results in your SOLO searches as the history of civil law jurisdictions is not the preserve of the LawBod's collection development: you may well find yourself visiting one or more the Bodleian's history Reading Rooms.