AAPC doesn't sponsor externship opportunities, but they do ask for and encourage externships and mentoring for their members. Many community college programs in billing/coding have access to practices and hospitals that offer externships, so you could start there. You could also ask at your local chapter meeting, or call local hospitals and practices to simply ask.
Externships seem like a great idea, but the logistics such as HIPAA, the lack of bandwidth to assign a mentor for an extern, and the lack of coding roles that are purely entry-level have caused the externship opportunities to virtually dry up. I think 2002 was the last time I was involved with a coding extern. She simply sat and observed for several weeks and we never got another one, because the manager at the time didn't feel we had the kind of work an extern could do. But that was us.
Your best use of time IMO, is to look for an entry level role.