I assume by “eurorail timetable” you mean the abbreviated timetable that came with your railpass?  It lists a small fraction of the available trains — probably less than 1/2 of the trains between the small percentage of cities that are listed, and it doesn’t list smaller cities and towns at all.

Use the German rail site for schedules anywhere in Europe.  It’s the most complete and the most user friendly in English. http://reiseauskunft… Click on the train you want (or check “details for all”) to see the connections.

All the trains on this route require connections.  Your best bet is to leave from Avignon Centre as opposed to Avignon TGV station — that will avoid a bus or regional train between those two stations.  You’ll end up on a regional train between Port Bou and Barcelona.  Only the part between Centre and Port Bou will actually require a reservation.  However, just go to the reservations office with a piece of paper that shows Avignon with the time you want to leave and then an arrow to Barcelona and the time you arrive.  Show them your railpass.  If you do need additional reservations they will sell you all the reservations at once or will put it all on one reservation card.

I travelled Barcelona – Montpellier (direct train with some stops); and then caught another train to Avignon from there. I’d assume you can do this in the opposite direction as well – check the site that oldlady provided the link to.