Hi Jim,
Another excellent book.

'Cierva Autogyros' by Peter W. Brooks
Smithsonian Institution Press

It is not only about Cierva gyros but it describes & has pics of almost every autogyro ever designed. Even has Registration #s & last known locations. Another gyronut told me about it.
I got mine from Strand Books in New York City.
It is a must have book.

Good luck,
Bob Gardner