Paris is listed and I had no trouble finding the schedule and price on Renfe.
Go to this page: http://www.renfe.com/EN/viajeros/
That is in English and stays in English. Choose " outward journey" instead of " return". Type Paris in the Departure box and when various choices pop up, choose Paris. Then type Barcelona in the Deatination section and choose Barcelona. The asterisk just means "all stations" and it will automatically pick the right one. (FWIW, it is Gare de Lyon and Barcelona Sants).
Then pick a date and hit "Buy". I chose 3 March and it showed two departures from Paris, at 7:15 and 14:07. Each takes 6.5 hours. Pick one and hit Continue. Next page will show the price for that date in 2d class (€97.90) and 1st class (€99). On the next page you have an opportunity to specify special fares ( youth, senior, etc.) if you qualify. Pick a fare and again hit Continue. The next page is where you enter your personal details and payment. Of course if you are just researching and not buying you would stop before this step.
As for registering on the site, I found that was not only unnecessary but actually an impediment to purchasing tickets. I did register but kept getting an error message with later attempts to purchase. So I went ahead and purchased our tickets for six separate journeys without logging in and with no difficulty. The tickets popped up in PDF format and I was able to print them out, no problem. That was two years ago and maybe the register/login function works better now, but if you are having trouble just go ahead to the purchase area.
Edit:when I view this reply on my iPad, part is in italics and the asterisks are missing. In case itis not clear, use " Paris* " and " Barcelona* " as the stations to make it easier. Or choose Paris Gare de Lyon and Barcelona Sants.