This isn't tailored for travel to Ferrol but the information is here.
Probably the closest airport with international flights to USA is Porto Portugal.
ANA manages Porto Airport (OPO)
http://www.ana.pt/en-US/Pages/Homepage.aspx
1900 Galicia, including Santiago, Sarria, and Fisterra
1901. This section discusses transportation options in Galicia
Index 1900
1902 Trains in Galicia
1903 Buses in Galicia
1904 Santiago
1905 Sarria
1906 Fisterra/Finisterre
1907 Muxia
1908 Vigo
1909 A Coruña
1910 Tui
1902
Trains in Galicia
-Renfe provides service Vigo to Valenca Portugal
-Renfe provides service to Santiago
-Renfe provides service to Sarria
Renfe
http://www.renfe.com/index.html
Map showing Renfe train network in Galicia
http://www.sarria.es/pdf/horarios-trenes.pdf
Renfe FEVE trains (Ferrol to Oviedo and Ferrol to Gijon)
http://www.renfe.com/EN/viajeros/feve/index.html
Comboios Celta train (Comboios de Portugal) (CP) connects Vigo Spain with Porto Portugal
http://www.cp.pt/cp/displayPage.do?vgnextoid=87cbd5abe2a74010VgnVCM1000007b01a8c0RCRD
1903
Buses in Galicia
Autna provides bus service from Vigo Spain to Porto Portugal.
http://www.autna.com/es/
Monbus provides bus service from Santiago to Fisterra (Finisterre), Vigo, and A Coruña.
Monbus provides bus service from Lugo to Sarria
http://www.monbus.es/index2.htm
Empresa Freire provides bus service from Santiago to Santiago Airport and Lugo.
http://www.empresafreire.com/html/castelan/seccion0.php
ATSA (not ALSA) provides several buses daily between Tui and Vigo. ATSA does not have a website. See Vigo Bus Station website for Schedule.
Autocares Vazquez ... service to Finisterre, Muxia, A Coruna, Santiago.
http://autocaresvazquez.net/index.asp
1904
Santiago
Santiago Renfe Station
http://www.adif.es/es_ES/infraestructuras/estaciones/31400/informacion_000050.shtml
Estacion de Autobuses Santiago
http://www.tussa.org/web/interior.php?txt=arbore_web5&lg=cas
Santiago Airport (SCQ) Labacolla (with flights to London, Frankfurt, et al)
http://www.aena-aeropuertos.es/csee/Satellite/Aeropuerto-Santiago/en/Santiago.html
1908
Vigo
Vigo Renfe Station
http://www.adif.es/es_ES/infraestructuras/estaciones/22308/informacion_000390.shtml
Vigo Airport (VGO) (with flights to Paris)
http://www.aena-aeropuertos.es/csee/Satellite/Aeropuerto-Vigo/en/Vigo.html
Vigo Bus Station
http://vigobus.com/
Vigo urban bus service connects to Vigo Airport
http://www.vitrasa.es/php/index.php
See 'calculo de rutas, horarios y lineas' in top left corner of Vitrasa site. Use the 'Parada' tab. Ferrocarril (train) is station 20057, Bus station is 5050, Airport Peinador is 14228. This will render schedule and transfer points.
1909
A Coruña
A Coruña Renfe Station
http://www.adif.es/es_ES/infraestructuras/estaciones/31412/informacion_000051.shtml
A Coruña Airport (LCG) (with flights to Lisbon)
http://www.aena-aeropuertos.es/csee/Satellite/Aeropuerto-A-Coruna/en/
A Coruña local bus connects airport to Puerta Real (downtown) on line 443 (Horarios tab)
http://www.autoscalpita.es/calidad.php
Busurbano information about buses in A Coruna ... (tab aeropuerta for line to airport) It shows airport, bus station and train station.
http://busurbano.info/
A Coruña bus station information
http://www.coruna.es/servlet/Satellite?c=Page&pagename=Portal/Page/Portal-ListadoBusesInterUrbanos&cid=1160564892240