As the title says, I'm looking for books on budgie mutations and breeding (assuming they go hand-in-hand). I've been looking around but most books seem to be about 'budgies/budgie care for beginners', which is not precisely what I'm after.
Have you read the information on CuteLittleBirdies website regarding breeding and mutations?
That would be a good place to start until other members offer you some actual book titles.
She also has an e-book about breeding available for sale through her site.