As it appears you are in Spain, the best (and only) option is to go to your nearest main station and buy the reservations there.

The Spain-France TGV is expensive for passholder reservations, cheaper but slower options are available, indeed it is possible to make the journey on reservation free trains without paying anything more.

Thank you so much for your quick response this was incredibly helpful. Just for clarification this means I have to go to a major train station to book a reservation. Also there are not independent travel agents who can help me with this, is this correct? Do you know if there are time limits for example do I need to do this 24 hours in advance? Or can I take my chances and just go and book the reservation an hour or so before my train leaves.   I understand the longer I wait there is a chance that the train will be completely booked. Once again thank you so much for your quick response.

You can book at any time in advance at the station, but when you do it is entirely up to you - Trains from Barcelona to France are notoriously busy for pass holders so make sure you have a plan B if it is full.

International TGV trains have passholder quotas so it is entirely possible that it will sell out well in advance of departure.

I do not know of any independent agents that can sell Spanish passholder reservations, if there were any they would be quite well known here as it is very difficult to obtain these reservations outside of Spain.

Everyone is being so helpful I’m going to keep this thread going a bit longer with your permission.

The first two countries I am visiting are Spain and France which it appears are the most difficult for train reservations and cost of reservations using a global pass.

After this I will be visiting Belgium, the Netherlands, Germany Czech Republic, Austria and Switzerland and possibly Italy. From what I have read these countries will be easier as they do not place so many restrictions on Eurail global passes and are not so expensive with the reservations. Is this true or will all countries be equally difficult as Spain and France? Once again thank you so much for your help.

Many trains, except night trains, in these countries have only optional reservation and there are also a lot trains where reservations are impossible to make.

Thank you for your reply everyone is being so helpful.

when you write that in reservations are impossible to make do you mean that you do not need a reservation and so when you board the train you may not get a seat or do you mean that because the reservation is it possible to make you cannot take the train at all. Thank you for the generosity with your time and effort.

I mean that no reservation is necessary and not even possible to make. This is the case on most regional trains. 

If you avoid the Thalys (or Eurostar, or TGV) to travel to, in or between Belgium, the Netherlands and Germany almost all of it can be done without reservations. On all other trains in Belgium and the Netherlands it’s not even possible to reserve.

For your own comfort it might be adviseable to buy a modest seat reservation fee for the long distance trains in Germany (€4,5) and Austria (€3).

Cross border traffic via ICE between Germany and the NL and/or Belgium has had some serious hiccups the last months. But you can always travel by local trains.

This link sums it up quite nicely what you need to know for these countries:

But by then, you already did the hard part ;)