How to travel from New Orleans, LA TO SAN Sabastion, Spain

British Airways/Iberia/American Airlines alliance is the way to book a MSY-EAS single ticket. ( 2 stops)

You will have to check each airlines website to see which offers the best price for your travel dates

I would look for a direct transatlantic flight from your preferred airport to any city. Then look at getting to San Sebastián from there. Use Skyscanner, which has an "everywhere" search option.