The situation may have changed, but in 2015 it was reported that the only options for Spanish-language primary education in Cataluña were 34 private schools. However, the same article also observes that
La LOMCE establece que si alguien no puede inscribir a sus hijos en un colegio público en el que se estudie en castellano o en bilingüe, porque la administración autonómica no lo contempla, el Estado les permite matricularlos en un colegio privado y luego se compromete a pagar a la familia ese coste.
The [Act to Improve the Quality of Education] disposes that if someone cannot register their children in a public school which teachs in Spanish or bilingually, because the [local] administration doesn't support it, the State allows them to register in a private school and commits itself to reimbursing that cost to the family.
It's slightly outside their remit, but you could try contacting the Catalan Assembly for Bilingual Education (see the second link above) to see whether they can give you updated information.
Update: as of 2018-04-05, the Tribunal Constitucional has thrown out the relevant part of the LOMCE.