Re: Developing courage
Many of the koryu arts spend a great deal of time training just that, the mental side. Read the "Life Giving Sword" to get a little taste of this. Mind you, reading the book won't help you get what you want but it should help you understand what the training is doing. You really need to be brought up through the kata with a skilled teacher who can challenge you and push your boundaries during training.
I have personally seen the benefit of this sort of training. I've been in situations where EVERYONE else around me freezes and I have not. It is sort of like when you are about to get the adrenal dump before a fight or flight response and instead it doesn't happen and you move very clearly and with great focus. I'm sorry if that sounds a little silly but that is the only way I can describe it.
There is a good article in "Koryu Bujutsu: Classical Warrior Traditions of Japan, volume 1" titled "Marishiten: Buddhist Influences on Combative Behavior" by David A. Hall. It is a short version of his PHD work on the subject which can also be purchased from the University of Hawaii.
I guess at the end of the day it is a lot of really hard, focused practice that challenges you past your comfort levels the entire time to push your limits and boundaries. I don't see why you can't do that in a good aikido class if you have a teacher who is willing to take ukemi for you to really challenge you.