Where should I go to get a foot orthotic?

See a podiatrist. I recommend seeing a podiatrist to have your feet evaluated and to see what type of orthotic is needed for your particular problem or if even an orthotic is the best treatment for your condition.
A Podiatrist. Podiatrists will cast you, and make sure they fit you well and fix them if they need adjustment.
Orthotic. See your podiatrist who will evaluate you and determine the proper device for you.