Given the number of different manufacturers that there were in Spain during the 1950s and 1960s, it is surprising how limited the choice of reference sources is.
In The Illustrated Encyclopedia of Motorcycles by Erwin Tragatsch, the dependable Tragatsch mentions many Spanish brands but without any real detail.
The Encyclopedia of Motorcycles by Roger Hicks is a very large book running to 544 pages. It can be found very cheaply on Abe Books but keep an eye on the postage costs.
The main reference sources that I have found to be helpful are, unsurprisingly, all Spanish but still there are not that many. An added complication is that some of them are now out of print and can only be bought second hand. Their scarcity is increasingly reflected in their rising prices. These are ones that I would recommend obtaining, if possible:
Enciclopedia de la Motocicleta Espanola (3 Volumes A-K, L-Q, R-Z) – Francisco HERREROS – published by Moto Retro
Historia del Motociclismo en Espana – Francisco HERREROS – published by RACC
Micromotores, Ciclomotores y Velomotores de la posguerra española – Francisco HERREROS – published by Moto Retro
Hispano Villiers – Francisco HERREROS – published by Moto Retro
Motos de la Posguerra – published by Museu Bassella and available via the Museum Shop.
La Moto Catalana – published by Museu Bassella and available via the Museum Shop.
Microcoches Espanoles – This book is primarily about Microcars but it has details of Motocarros. It can be bought through the Classic Motor Club del Bages at Manresa.
This is a link to an excellent and expanding Spanish site that specializes in old Catalogues and publicity material. https://sites.google.com/view/catalogosmotocicletasesp/presentaci%C3%B3n
This is a great site and covers bikes, motocarros and sidecars from around the world.
Spanish Motorcycles 