Yes I too agree with above suggestions that any kind of poetry or novels which has lots of dialogues are best to practice crutch 8.
I would also like to add to this a way to practice crutch 8. The way is when you are reading a book or poem read a lines or a dialogue, keep it in your mind and speak it in front of a mirror by looking at yourself while using crutch 8. Use passion and body language to the maximum while speaking the lines. This will help you easily modulate your voice as you are not just reading but speaking the lines like you are doing an act on a stage like an actor.