Try your local community college. Because there are scams associated with medical billing you need to get someone that has a legitimate back ground in it (why I suggest the community college as a first start). Take a course, but ask the teacher if s/he can supply a list of legitimate businesses that you can work for before during or after the course.

I do not suggest that you go to your doctor looking for work, but I do suggest you ask them who they use- might give you a place to start looking.

Good luck,
Guard5a