Do you think you could handle a job with very little customer interaction if you could get past the interview? Maybe you could read up on some prospects that require other skills that you can hold down while you work on anxiety, too. That's specific, and I hear people do better with specific goals and plans than vague ones.
I don't know of any free resources, though CBT (cognitive behavioral therapy) is supposed to have some online. Maybe another member can chime in with something.