I just put up a thread on my experience this past week brewing root beer only using roots, herbs, and spices.
I did have a hard time finding recipes, but pieced things together over time and gave it a shot. The recipe still needs a few tweeks, but what I brewed tastes great.
I was able to purchase everything between my own LHBS and the supermarket. I believe most of it could also be sourced with northern brewer or midwest as well.