I have the book Gendarmerie en Espagne et au Portugal
It is very accurate, dealing with the organization, fights, and fate of each legion de gendarmerie, with a few nice pictures.
It is much focused on the events in northern Spain (Navarre, Biscaye, Aragon, Catalogne).
No big battle here, but a vivid look on the sysyphe work of holding the roads open from France to Spain. It shows very well how the guerilla strenghened each year.
Of course, a clear bias in favour of French.