I'm afraid that one always sells out to (season ticket owners and) club card holders. You'll have to resort to ticket scalpers. Perhaps someone on here can point you to a trustworthy site that doesn't completely suck you dry.
VALENCIA: Neto - Montoya, Garay, Gabriel Paulista, Gayà - Carlos Soler, Kondogbia, Parejo, Guedes - Rodrigo Moreno, Zaza.
BARCELONA: Ter Stegen - Semedo, Vermaelen, Umtiti, Jordi Alba - Rakitic, Busquets - Messi, Paulinho, Iniesta - Suárez.
vermaelen and paulinho in the lineup and not a single player on the bench worth putting in. just like you always dreamed of going into the toughest away game in the league