I find little bits and pieces here and there. Some of the best information about components is available from parts manufacturers themselves. There are lots of documents scattered here and there that show the manufacturing process of specific components and why they chose that type. As for amp circuits, it's kind of the same thing. You'll find one source that is very informative about one or two topologies, because that's what they've focused on. But they won't have much to say about any of the others. You just have to root around.