Please mention travel date and departure time.

If you mean the new Renfe AVE, then Deutsche Bahn might be able to sell it, but then only at the ticket office or by phone.

Sat 23/09 12.35 from Nimes TGV

Sat 23/09 09.58 from Narbonne AVI 

I can't find any train at 12:35 from either station in Nîmes. Do you mean from Nice maybe?

9:58 from Narbonne doesn't make any sense if you're departing from Nice at 12:35 and want to travel to Barcelona.

Could you please post your complete timetable for that day?

I’m considering two options:

1. NICE VILLE (8.25) - BARCELONA CITY (SPAIN) 23/09 via MARSEILLE ST CHARLES and NIMES (12:47) - for which I cannot do a reservation
2. NICE VILLE - CARCASSONNE and then CARCASSONNE (18:27) - BARCELONA-SANTS via NARBONNE (19:23) for which I cannot do a reservation

Please sb help me

Option 1 is better this way, since you'll have more time to change train in Narbonne than in Nîmes:

Reservations are €10 for Marseille-Narbonne, and €25 for Narbonne-Barcelona. Both can be booked on interrail.eu (€2 booking fee per person and train), but there's currently a problem with booking 2nd class there. Either wait a few days until they solve this issue or call SNCF (#85 for English, no booking fee).

You can also travel reservation-free (it will then take all day though), or limit it to €10 for Marseille-Narbonne with this option:

Option 2:

Nice-Carcassonne would be €10 (supposing you leave Nice at the same time).

Carcassonne-Narbonne is €20.

Narbonne-Barcelona €25.

To book, the same applies as for option 1.