Have you joined the American Iris Society yet? They send you a book called The World of Irises...by many authors. There is a little bit about hybridizing there.
Another book that I found somewhat useful...the reason "somewhat" is because the book is so old and the varieties mentioned are too, but still informative, is called "Iris Culture and Hybridizing For Everyone" by Wilma L. Vallette 1961
It takes time to find books on iris hybridizing, but there are a few out there.
