I did not have anything booked out of Santiago until my actual arrival in Santiago itself, at which time I booked a flight to Barcelona (I think it was about 60Euros). It is very easy and not too pricey at all to make last minute arrangements. Once you get within your final few days on the Camino, and know when you'll be arriving in Santiago, I'd say just hop on the internet somewhere and look at flights options. If you'd rather take a train, I'd recommend the RENFE website, which you can either book once you arrive in Santiago or a few days ahead, whatever you prefer. During some free time in Santiago, I strolled over to the train station and just bought my tickets at a machine for a next day trip to A Coruña.
Of course, I guess to answer your original thought...I don't know any travel assistance places :roll: Oops. But it's very easy if you want to do it yourself!
Have a fantastic journey, buen camino.
P.S. Do you live in SF? I live in Santa Rosa...