After much google-ing I have found the official online timetable of the bus services between Pamplona and Roncesvalles: http://www.autocaresartieda.com/default.html . I think it works with "pop-ups" as once you reach this page you then have to click on "linaes regulares" and then select the Jaurrieta-Pamplona service. Lots of services are listed; clicking on the details button at the far right edge gives the info about the days of the week that the service runs and the dates between which the details are or were valid. The site is only in Spanish and Euskara, but I found the Spanish version OK to follow.
While there seem to be quite a few buses between the two towns, most details are historic. The morning buses were from summer 2007 and are not running at the moment. Until 2nd July 2008 the only buses are 1600 on Saturdays, arriving 17.10; and 1800 Mon - Fri, arriving 19.10.
At the time of this post, there are no details for dates after 2 July 2008, but the link above looks like it should work after that.
While there seem to be quite a few buses between the two towns, most details are historic. The morning buses were from summer 2007 and are not running at the moment. Until 2nd July 2008 the only buses are 1600 on Saturdays, arriving 17.10; and 1800 Mon - Fri, arriving 19.10.
At the time of this post, there are no details for dates after 2 July 2008, but the link above looks like it should work after that.