I have purchased wool clothing from goodwill and plan to over-dye it. I purchased a coat for $4. The only drawback is I have not found white or light wool yet.
I've looked around at fiber fairs, wool felt in quilt shops and online. The weight of the wool varies and it is a bit expensive. The best way to evaluate online sites is to get a few pieces and see if you like the colors and weights of the fabric.