Theoretically yes, but in practice no. There are very few high speed trains from France to Spain (currently only 2 per day) and they have only a limited number of seats for pass holders. If there are still pass holder seats available, then you can surely buy one but in practice, they sell out several days in advance. If I check the trains from tomorrow (6 March) then the first train with available seats for pass holders is on 12 March. So it is unlikely that there will still be a pass holder seat left on the day for this train.

Do you stay in Paris or anywhere else in Europe before taking the train to Barcelona? Could you have it delivered there?

OR B smarter and go via changes and local TGV INside FR only-has been explained here many times! Like to Perpignan or Montpellier.

Also you do not need to be in Paris to get this REServ-can do @ any SNCF counter.

In which countries I can find a SNCF counter? I thought it was France only?

We need to travel from Barcelona to Paris on august 8, 2022, how can we get seat reservations ? Online I can’t book them, is that because sold out or  because in Spain you need to go to station to get these reservations? We have eurrail pass for that day.

You could call SNCF call center, if there are seat left for Pass users than you can get if via email as e-reservation from them. Or at the ticket office of RENFE (theoretical possible at any RENFE Ticket Offices).