also, keep in mind that in SJPP they give you the information that you need (maps, layout of the land, location of water, phone numbers and locations of albergues). I didn't actually go with a guidebook, and ended up with one about 10 days in because someone for some reason brought 3, and gave me one. Even if you don't have a guidebook and want info in addition to what you are given at the start, you can look on someone else's book.
I don't recall there being anywhere to buy anything in Roncesvalles. There is really nothing there. A place to get your credential, a small bar/restaurant, and the monistary/albergue. But, maybe I am mistaken. However, you will be passing through Pamplona on your 3rd day or so and you can definately buy a guide book there. I also have heard that the El Paiz book is the best one out there, even though it is in spanish.
you are from Galway?? I was living there this past year, until I started my camino in April!