Where to fly to
Hola Magnara,
I know that is is difficult to plan the best travel arrangements when yiou are so far away. However, there is no direct and easy way to get to either St Jean or Roncesvalles - both involve flights, train, bus and/or taxi. Remember that one is in France - the other in Spain - so there are no trains between the two or busses.
Roncesvalles is not a town, it is a monastery complex with a Church, Monastery, hostel, a couple of inns and very little else. If you want to start in Roncesvalles then Madrid would be the place to fly to.
You would then get a train or bus to Pamplona and the evening bus to Roncesvalles.
If you want to start in St Jean you can still fly to Madrid - follow the train/bus to Pamplona and bus to Roncesvalles and get a taxi over to St Jean.
Or you can fly to Bilbao and follow this route.
Bilbao to St Jean: Coach service to Hendaye. Ticket and bus stop at Termibus by the Hospital Civile de Basuto. 1.hr 50mins €7. From Hendaye to St Jean by train via Bayonne 3 ½ hours
http://www.sncf.com (French Rail)
Once you are there is is less complicated and then you just have to follow the yellow arrows and put one foot in front of the other for ± 800kms!
Let us know what you decide.